Performing C SOURCE FILE Test ARCH_X86_64 failed with the following output:
Change Dir: /usr/lfs/v0/rc-buildroot-test/scripts/instance-1/output/build/fastd-18/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/gmake" "cmTC_29e1e/fast"
gmake[1]: Entering directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-1/output/build/fastd-18/CMakeFiles/CMakeTmp'
/usr/bin/gmake -f CMakeFiles/cmTC_29e1e.dir/build.make CMakeFiles/cmTC_29e1e.dir/build
gmake[2]: Entering directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-1/output/build/fastd-18/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_29e1e.dir/src.c.o
/usr/lfs/v0/rc-buildroot-test/scripts/instance-1/output/host/bin/i586-linux-gcc --sysroot=/usr/lfs/v0/rc-buildroot-test/scripts/instance-1/output/host/i586-buildroot-linux-musl/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os -DARCH_X86_64  -DNDEBUG   -o CMakeFiles/cmTC_29e1e.dir/src.c.o   -c /usr/lfs/v0/rc-buildroot-test/scripts/instance-1/output/build/fastd-18/CMakeFiles/CMakeTmp/src.c
/usr/lfs/v0/rc-buildroot-test/scripts/instance-1/output/build/fastd-18/CMakeFiles/CMakeTmp/src.c:3:2: error: #error not x86_64
 #error not x86_64
  ^~~~~
gmake[2]: *** [CMakeFiles/cmTC_29e1e.dir/src.c.o] Error 1
gmake[2]: Leaving directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-1/output/build/fastd-18/CMakeFiles/CMakeTmp'
gmake[1]: *** [cmTC_29e1e/fast] Error 2
gmake[1]: Leaving directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-1/output/build/fastd-18/CMakeFiles/CMakeTmp'

Source file was:

#ifndef __x86_64__
#error not x86_64
#endif

int main() {return 0;}