add optional dnsmasq features to cmake

[darkexplosiveqwx]

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What does this PR aim to accomplish?:

Allow to enable build-time dnsmasq features if the development headers / libraries are present.

I am using Fedora 42 and the cmake RPM macro presets from %cmake and %cmake_build
Compilation works:

$ /usr/bin/cmake         -S "."         -B "redhat-linux-build"         -DCMAKE_C_FLAGS_RELEASE:STRING="-DNDEBUG"         -DCMAKE_CXX_FLAGS_RELEASE:STRING="-DNDEBUG"         -DCMAKE_Fortran_FLAGS_RELEASE:STRING="-DNDEBUG"         -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON         -DCMAKE_INSTALL_DO_STRIP:BOOL=OFF         -DCMAKE_INSTALL_PREFIX:PATH=/usr         -DCMAKE_INSTALL_FULL_SBINDIR:PATH=/usr/bin         -DCMAKE_INSTALL_SBINDIR:PATH=bin         -DINCLUDE_INSTALL_DIR:PATH=/usr/include         -DLIB_INSTALL_DIR:PATH=/usr/lib64         -DSYSCONF_INSTALL_DIR:PATH=/etc         -DSHARE_INSTALL_PREFIX:PATH=/usr/share
-- The C compiler identification is GNU 15.2.1
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/lib64/ccache/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Compiling dynamically linked executable
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE
-- Looking for sys/random.h
-- Looking for sys/random.h - found
-- Looking for unwind.h
-- Looking for unwind.h - found
-- Building FTL with _Unwind_Backtrace support: YES
-- Looking for libnetfilter_conntrack/libnetfilter_conntrack.h
-- Looking for libnetfilter_conntrack/libnetfilter_conntrack.h - found
-- Building FTL with dnsmasq conntrack support: YES
-- Looking for nftables/libnftables.h
-- Looking for nftables/libnftables.h - found
-- Building FTL with dnsmasq nftset support: YES
-- Found PkgConfig: /usr/bin/pkg-config (found version "2.3.0")
-- Found DBus: /usr/include/dbus-1.0;/usr/lib64/dbus-1.0/include
-- Building FTL with dnsmasq DBus support: YES
-- Building FTL with readline support: YES
-- Building FTL with TLS support: NO
-- Configuring done (1.9s)
-- Generating done (0.1s)
CMake Warning:
  Manually-specified variables were not used by the project:

    CMAKE_CXX_FLAGS_RELEASE
    CMAKE_Fortran_FLAGS_RELEASE
    CMAKE_INSTALL_DO_STRIP
    CMAKE_INSTALL_FULL_SBINDIR
    CMAKE_INSTALL_SBINDIR
    INCLUDE_INSTALL_DIR
    LIB_INSTALL_DIR
    SHARE_INSTALL_PREFIX
    SYSCONF_INSTALL_DIR


-- Build files have been written to: /home/shared/Projects/fleet/pi-hole-FTL/redhat-linux-build
$ /usr/bin/cmake --build "redhat-linux-build" -j6 --verbose
[...]
$ /home/shared/Projects/fleet/pi-hole-FTL/redhat-linux-build/pihole-FTL -vv
****************************** FTL **********************************
Version:         v6.6.1-189-g590733e7-dirty
Branch:          development
Commit:          590733e7-dirty (2026-04-30 18:34:59 +0200)
Architecture:    x86_64 (compiled locally)
Compiler:        gcc (GCC) 15.2.1 20260123 (Red Hat 15.2.1-7)
GLIBC version:   2.42

****************************** dnsmasq ******************************
Version:         pi-hole-v2.92rc1
Features:        IPv6 GNU-getopt DBus no-UBus no-i18n IDN2 DHCP DHCPv6 Lua TFTP conntrack ipset nftset auth DNSSEC loop-detect inotify dumpfile

****************************** SQLite3 ******************************
Version:         3.51.3
Features:        ATOMIC_INTRINSICS=1 COMPILER=gcc-15.2.1 20260123 (Red Hat 15.2.1-7) DEFAULT_AUTOVACUUM DEFAULT_CACHE_SIZE=4096 DEFAULT_FILE_FORMAT=4 DEFAULT_FOREIGN_KEYS DEFAULT_JOURNAL_SIZE_LIMIT=33554432 DEFAULT_MEMSTATUS=0 DEFAULT_MMAP_SIZE=0 DEFAULT_PAGE_SIZE=4096 DEFAULT_PCACHE_INITSZ=20 DEFAULT_RECURSIVE_TRIGGERS DEFAULT_SECTOR_SIZE=4096 DEFAULT_SYNCHRONOUS=1 DEFAULT_WAL_AUTOCHECKPOINT=1000 DEFAULT_WAL_SYNCHRONOUS=1 DEFAULT_WORKER_THREADS=0 DIRECT_OVERFLOW_READ DQS=0 ENABLE_CARRAY ENABLE_DBPAGE_VTAB ENABLE_EXPLAIN_COMMENTS ENABLE_PERCENTILE LIKE_DOESNT_MATCH_BLOBS MALLOC_SOFT_LIMIT=1024 MAX_ATTACHED=10 MAX_COLUMN=2000 MAX_COMPOUND_SELECT=500 MAX_DEFAULT_PAGE_SIZE=8192 MAX_EXPR_DEPTH=1000 MAX_FUNCTION_ARG=1000 MAX_LENGTH=1000000000 MAX_LIKE_PATTERN_LENGTH=50000 MAX_MMAP_SIZE=0x7fff0000 MAX_PAGE_COUNT=0xfffffffe MAX_PAGE_SIZE=65536 MAX_SQL_LENGTH=1000000000 MAX_TRIGGER_DEPTH=1000 MAX_VARIABLE_NUMBER=32766 MAX_VDBE_OP=250000000 MAX_WORKER_THREADS=8 MUTEX_PTHREADS OMIT_DEPRECATED OMIT_LOAD_EXTENSION OMIT_PROGRESS_CALLBACK OMIT_SHARED_CACHE SYSTEM_MALLOC TEMP_STORE=1 THREADSAFE=1

******************************** LUA ********************************
Version:         Lua 5.5.0
Libraries:       inspect.lua (8.27 kB) 

***************************** LIBNETTLE *****************************
Version:         3.10
GMP:             Full

****************************** CivetWeb *****************************
Version:         1.17 (modified by Pi-hole) without mbed TLS
Features:        Files: Yes, TLS: No, CGI: No, IPv6: Yes, 
                 WebSockets: No, Server-side JavaScript: No
                 Lua: Yes, Cache: Yes, Stats: No, Compression: No
                 HTTP2: No, Unix domain sockets: No

****************************** cJSON ********************************
Version:         1.7.18

Absence is correctly detected:

$ /usr/bin/cmake         -S "."         -B "redhat-linux-build"         -DCMAKE_C_FLAGS_RELEASE:STRING="-DNDEBUG"         -DCMAKE_CXX_FLAGS_RELEASE:STRING="-DNDEBUG"         -DCMAKE_Fortran_FLAGS_RELEASE:STRING="-DNDEBUG"         -DCMAKE_VERBOSE_MAKEFILE:BOOL=ON         -DCMAKE_INSTALL_DO_STRIP:BOOL=OFF         -DCMAKE_INSTALL_PREFIX:PATH=/usr         -DCMAKE_INSTALL_FULL_SBINDIR:PATH=/usr/bin         -DCMAKE_INSTALL_SBINDIR:PATH=bin         -DINCLUDE_INSTALL_DIR:PATH=/usr/include         -DLIB_INSTALL_DIR:PATH=/usr/lib64         -DSYSCONF_INSTALL_DIR:PATH=/etc         -DSHARE_INSTALL_PREFIX:PATH=/usr/share
-- The C compiler identification is GNU 15.2.1
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/lib64/ccache/cc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Compiling dynamically linked executable
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE
-- Looking for sys/random.h
-- Looking for sys/random.h - found
-- Looking for unwind.h
-- Looking for unwind.h - found
-- Building FTL with _Unwind_Backtrace support: YES
-- Looking for libnetfilter_conntrack/libnetfilter_conntrack.h
-- Looking for libnetfilter_conntrack/libnetfilter_conntrack.h - not found
-- Building FTL with dnsmasq conntrack support: NO
-- Looking for nftables/libnftables.h
-- Looking for nftables/libnftables.h - not found
-- Building FTL with dnsmasq nftset support: NO
-- Found PkgConfig: /usr/bin/pkg-config (found version "2.3.0")
-- Could NOT find DBus (missing: DBUS_INCLUDE_DIRS DBUS_LIBRARIES) 
-- Building FTL with dnsmasq DBus support: NO
-- Building FTL with readline support: YES
-- Building FTL with TLS support: NO
-- Configuring done (1.1s)
-- Generating done (0.1s)
CMake Warning:
  Manually-specified variables were not used by the project:

    CMAKE_CXX_FLAGS_RELEASE
    CMAKE_Fortran_FLAGS_RELEASE
    CMAKE_INSTALL_DO_STRIP
    CMAKE_INSTALL_FULL_SBINDIR
    CMAKE_INSTALL_SBINDIR
    INCLUDE_INSTALL_DIR
    LIB_INSTALL_DIR
    SHARE_INSTALL_PREFIX
    SYSCONF_INSTALL_DIR


-- Build files have been written to: /home/shared/Projects/fleet/pi-hole-FTL/redhat-linux-build

How does this PR accomplish the above?:

The change in FindDBus.cmake is necessary, otherwise CMake will complain with:

-- Building FTL with dnsmasq nftset support: YES
-- Found PkgConfig: /usr/bin/pkg-config (found version "2.3.0")
CMake Warning (dev) at /usr/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:441 (message):
  The package name passed to `find_package_handle_standard_args` (DBUS) does
  not match the name of the calling package (DBus).  This can lead to
  problems in calling code that expects `find_package` result variables
  (e.g., `_FOUND`) to follow a certain pattern.
Call Stack (most recent call first):
  src/FindDBus.cmake:59 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
  src/CMakeLists.txt:400 (find_package)
This warning is for project developers.  Use -Wno-dev to suppress it.

-- Found DBUS: /usr/include/dbus-1.0;/usr/lib64/dbus-1.0/include
-- Building FTL with dnsmasq DBus support: YES

I have also removed the reference to DNSMASQ_ALL_OPTS, a quick rg yielded no other matches.
It was originally added in #1472, but the associcated CMake part was removed in #1962 (github blame only a bit helpful when searching for removed lines).
With now being able to enable the features one-by-one this is no longer needed.

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[darkexplosiveqwx]

Some questions:
Do we want the features to be ON or OFF by default?
We don't want to add a library if they happen to have the -devel, but not the runtime library and let it fail on startup.
But D-Bus and especially libnftables are installed on almost every Linux distro (for runtime).
Conntrack should also work fine: (from src/dnsmasq/config.h)

HAVE_CONNTRACK
   define this to include code which propagates conntrack marks from
   incoming DNS queries to the corresponding upstream queries. This adds
   a build-dependency on libnetfilter_conntrack, but the resulting binary will
   still run happily on a kernel without conntrack support

And should I call it Building FTL with dnsmasq nftset support or Building FTL with nftset support?