Atomics check is wrong: HAVE_CXX_ATOMICS_WITHOUT_LIB succeeds on a platform where 8-byte atomics are not supported without `libatomic`

[barracuda156]

There is something wrong with the check. It must fail on ppc, but it succeeds:

--->  Configuring fizz
Executing:  cd "/opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_devel_fizz/fizz/work/build" && /opt/local/bin/cmake -G "Ninja" -DCMAKE_BUILD_TYPE=MacPorts -DCMAKE_INSTALL_PREFIX="/opt/local" -DCMAKE_INSTALL_NAME_DIR="/opt/local/lib" -DCMAKE_SYSTEM_PREFIX_PATH="/opt/local;/usr" -DCMAKE_C_COMPILER="$CC" -DCMAKE_CXX_COMPILER="$CXX" -DCMAKE_OBJC_COMPILER="$CC" -DCMAKE_OBJCXX_COMPILER="$CXX" -DCMAKE_POLICY_DEFAULT_CMP0025=NEW -DCMAKE_POLICY_DEFAULT_CMP0060=NEW -DCMAKE_VERBOSE_MAKEFILE=ON -DCMAKE_COLOR_MAKEFILE=ON -DCMAKE_FIND_FRAMEWORK=LAST -DCMAKE_EXPORT_COMPILE_COMMANDS=ON -DCMAKE_MAKE_PROGRAM=ninja -DCMAKE_MODULE_PATH="/opt/local/share/cmake/Modules;/opt/local/lib/libfmt10/cmake" -DCMAKE_PREFIX_PATH="/opt/local/share/cmake/Modules;/opt/local/lib/libfmt10/cmake" -DCMAKE_BUILD_WITH_INSTALL_RPATH:BOOL=ON -DCMAKE_INSTALL_RPATH="/opt/local/lib" -Wno-dev -DBUILD_TESTS=OFF -DBUILD_SHARED_LIBS=ON -DBOOST_ROOT=/opt/local/libexec/boost/1.81 -DBOOSTROOT=/opt/local/libexec/boost/1.81 -DBOOST_INCLUDEDIR=/opt/local/libexec/boost/1.81/include -DBOOST_LIBRARYDIR=/opt/local/libexec/boost/1.81/lib -DBOOST_INCLUDE_DIR=/opt/local/libexec/boost/1.81/include -DBOOST_LIBRARY_DIR=/opt/local/libexec/boost/1.81/lib -DBOOST_LIB_DIR=/opt/local/libexec/boost/1.81/lib -DBoost_NO_SYSTEM_PATHS=ON -DBoost_INCLUDE_DIR=/opt/local/libexec/boost/1.81/include -DBoost_DIR=/opt/local/libexec/boost/1.81 -DOPENSSL_ROOT_DIR=/opt/local/libexec/openssl3 -DOPENSSL_INCLUDE_DIR=/opt/local/libexec/openssl3/include -DWITH_SSL=/opt/local/libexec/openssl3 -DCMAKE_OSX_ARCHITECTURES="ppc" -DCMAKE_OSX_DEPLOYMENT_TARGET="10.6" -DCMAKE_OSX_SYSROOT="/" /opt/local/var/macports/build/_opt_PPCSnowLeopardPorts_devel_fizz/fizz/work/fizz-v2024.06.03.00/fizz 
-- The CXX compiler identification is GNU 13.2.1
-- The C compiler identification is GNU 13.2.1
-- Checking whether CXX compiler has -isysroot
-- Checking whether CXX compiler has -isysroot - yes
-- Checking whether CXX compiler supports OSX deployment target flag
-- Checking whether CXX compiler supports OSX deployment target flag - yes
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /opt/local/bin/g++-mp-powerpc - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Checking whether C compiler has -isysroot
-- Checking whether C compiler has -isysroot - yes
-- Checking whether C compiler supports OSX deployment target flag
-- Checking whether C compiler supports OSX deployment target flag - yes
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /opt/local/bin/gcc-mp-powerpc - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD
-- Performing Test CMAKE_HAVE_LIBC_PTHREAD - Success
-- Found Threads: TRUE
-- Found Boost: /opt/local/libexec/boost/1.81/include (found suitable version "1.81.0", minimum required is "1.51.0") found components: context filesystem program_options regex system thread chrono atomic
-- Found folly: /opt/local
-- Found OpenSSL: /opt/local/libexec/openssl3/lib/libcrypto.dylib (found version "3.1.5")
-- Found Glog: /opt/local/lib/libglog.dylib
-- Found gflags from package config /opt/local/lib/cmake/gflags/gflags-config.cmake
-- Found gflags as a dependency of glog::glog, include=/opt/local/include, libs=gflags_shared
-- Found LIBUNWIND: /opt/local/lib/libunwind.dylib
-- Found LibUnwind as a dependency of glog::glog, include=/opt/local/include, libs=/opt/local/lib/libunwind.dylib
-- Found DoubleConversion: /opt/local/lib/libdouble-conversion.dylib
-- Found ZSTD: /opt/local/lib/libzstd.dylib
-- Found Zstd: /opt/local/lib/libzstd.dylib
-- Performing Test HAVE_CXX_ATOMICS_WITHOUT_LIB
-- Performing Test HAVE_CXX_ATOMICS_WITHOUT_LIB - Success
-- Found Sodium: /opt/local/lib/libsodium.dylib
-- Found gflags from package config
-- Found ZLIB: /opt/local/lib/libz.dylib (found version "1.3.1")
-- Found libevent: /opt/local/lib/libevent.dylib
-- Could NOT find liboqs (missing: liboqs_DIR)
-- Configuring done (11.2s)
-- Generating done (0.1s)

Subsequently, that breaks linking, since -latomic is not passed.

FAILED: bin/fizz 
: && /opt/local/bin/g++-mp-powerpc -pipe -I/opt/local/libexec/openssl3/include -I/opt/local/libexec/boost/1.81/include -Os -DNDEBUG -I/opt/local/libexec/openssl3/include -isystem/opt/local/include/LegacySupport -I/opt/local/libexec/boost/1.81/include -isystem/opt/local/include -D_GLIBCXX_USE_CXX11_ABI=0 -arch ppc -mmacosx-version-min=10.6 -Wl,-search_paths_first -Wl,-headerpad_max_install_names -L/opt/local/libexec/openssl3/lib -L/opt/local/libexec/boost/1.81/lib -Wl,-headerpad_max_install_names -L/opt/local/lib -lMacportsLegacySupport CMakeFiles/FizzTool.dir/tool/Main.cpp.o CMakeFiles/FizzTool.dir/tool/FizzClientCommand.cpp.o CMakeFiles/FizzTool.dir/tool/FizzClientLoadGenCommand.cpp.o CMakeFiles/FizzTool.dir/tool/FizzCommandCommon.cpp.o CMakeFiles/FizzTool.dir/tool/FizzGenerateDelegatedCredentialCommand.cpp.o CMakeFiles/FizzTool.dir/tool/FizzServerBenchmarkCommand.cpp.o CMakeFiles/FizzTool.dir/tool/FizzServerCommand.cpp.o -o bin/fizz  -Wl,-rpath,/opt/local/lib  lib/libfizz.1.0.0.dylib  /opt/local/lib/libsodium.dylib  /opt/local/lib/libfolly.0.58.0-dev.dylib  /opt/local/lib/libfmt10/libfmt.10.2.1.dylib  /opt/local/libexec/boost/1.81/lib/libboost_context-mt.dylib  /opt/local/libexec/boost/1.81/lib/libboost_filesystem-mt.dylib  /opt/local/libexec/boost/1.81/lib/libboost_program_options-mt.dylib  /opt/local/libexec/boost/1.81/lib/libboost_regex-mt.dylib  /opt/local/libexec/boost/1.81/lib/libboost_system-mt.dylib  /opt/local/libexec/boost/1.81/lib/libboost_thread-mt.dylib  /opt/local/libexec/boost/1.81/lib/libboost_chrono-mt.dylib  /opt/local/libexec/boost/1.81/lib/libboost_atomic-mt.dylib  /opt/local/lib/libdouble-conversion.dylib  /opt/local/lib/libglog.dylib  /opt/local/lib/libevent.dylib  /opt/local/lib/libz.dylib  /opt/local/lib/libbz2.dylib  /opt/local/lib/liblzma.dylib  /opt/local/lib/liblz4.dylib  /opt/local/lib/libsnappy.dylib  /opt/local/lib/libsodium.dylib  /opt/local/lib/libunwind.dylib  /opt/local/libexec/openssl3/lib/libssl.dylib  /opt/local/libexec/openssl3/lib/libcrypto.dylib  /opt/local/lib/libz.dylib  /opt/local/lib/libzstd.dylib  /opt/local/lib/libgflags.2.2.2.dylib && :
Undefined symbols:
  "___atomic_fetch_add_8", referenced from:
      __ZN5folly18NamedThreadFactory9newThreadEONS_8FunctionIFvvEEE in FizzClientLoadGenCommand.cpp.o
      __ZN5folly18NamedThreadFactory9newThreadEONS_8FunctionIFvvEEE in FizzServerBenchmarkCommand.cpp.o
ld: symbol(s) not found
collect2: error: ld returned 1 exit status