It's no sense to repeat an already failed check.
Looks like a copy-paste bug as the HAVE_CXX_LIBATOMICS64_2ARGS test
runs again the very same check as the HAVE_LIBATOMIC_2ARGS.
Without this change the check obviously fails:
-- Performing Test HAVE_LIBATOMIC_2ARGS
-- Performing Test HAVE_LIBATOMIC_2ARGS - Failed
-- Performing Test HAVE_CXX_ATOMICS64_WITHOUT_LIB
-- Performing Test HAVE_CXX_ATOMICS64_WITHOUT_LIB - Failed
-- Looking for __atomic_load_8 in atomic
-- Looking for __atomic_load_8 in atomic - not found
-- Performing Test HAVE_CXX_LIBATOMICS64_2ARGS
-- Performing Test HAVE_CXX_LIBATOMICS64_2ARGS - Failed
CMake Error at cmake/CheckAtomic.cmake:146 (message):
Host compiler appears to require libatomic, but cannot find it.
Call Stack (most recent call first):
CMakeLists.txt:80 (include)
With this change the test HAVE_CXX_LIBATOMICS64_2ARGS succeeds:
-- Performing Test HAVE_LIBATOMIC_2ARGS
-- Performing Test HAVE_LIBATOMIC_2ARGS - Failed
-- Performing Test HAVE_CXX_ATOMICS64_WITHOUT_LIB
-- Performing Test HAVE_CXX_ATOMICS64_WITHOUT_LIB - Failed
-- Looking for __atomic_load_8 in atomic
-- Looking for __atomic_load_8 in atomic - not found
-- Performing Test HAVE_CXX_LIBATOMICS64_2ARGS
-- Performing Test HAVE_CXX_LIBATOMICS64_2ARGS - Success
-- Performing Test HAVE_CXX_ATOMICS64_WITH_LIB
-- Performing Test HAVE_CXX_ATOMICS64_WITH_LIB - Success
Use 'long long' in the check_working_cxx_atomics check.
Without it the check succeed but fails during linking:
-- Performing Test HAVE_CXX_ATOMICS_WITHOUT_LIB
-- Performing Test HAVE_CXX_ATOMICS_WITHOUT_LIB - Success
Tested with the following toolchains with OpenWrt:
* toolchain-aarch64_cortex-a72_gcc-8.3.0_musl
* toolchain-arm_cortex-a7+neon-vfpv4_gcc-8.3.0_musl_eabi
* toolchain-i386_pentium_gcc-8.3.0_musl
* toolchain-mips_24kc_gcc-8.3.0_musl
* toolchain-mipsel_24kc_gcc-8.3.0_musl
