Determining if the include file pthread.h exists failed with the following output:
Change Dir: /usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/bullet-3.09/CMakeFiles/CMakeTmp

Run Build Command(s):/usr/bin/gmake cmTC_ac3cf/fast && gmake[1]: Entering directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/bullet-3.09/CMakeFiles/CMakeTmp'
/usr/bin/gmake  -f CMakeFiles/cmTC_ac3cf.dir/build.make CMakeFiles/cmTC_ac3cf.dir/build
gmake[2]: Entering directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/bullet-3.09/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_ac3cf.dir/CheckIncludeFile.c.o
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/bin/arm-linux-gcc --sysroot=/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/host/arm-buildroot-linux-uclibcgnueabihf/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os   -DNDEBUG   -o CMakeFiles/cmTC_ac3cf.dir/CheckIncludeFile.c.o   -c /usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/bullet-3.09/CMakeFiles/CMakeTmp/CheckIncludeFile.c
/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/bullet-3.09/CMakeFiles/CMakeTmp/CheckIncludeFile.c:1:10: fatal error: pthread.h: No such file or directory
    1 | #include <pthread.h>
      |          ^~~~~~~~~~~
compilation terminated.
gmake[2]: *** [CMakeFiles/cmTC_ac3cf.dir/CheckIncludeFile.c.o] Error 1
gmake[2]: Leaving directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/bullet-3.09/CMakeFiles/CMakeTmp'
gmake[1]: *** [cmTC_ac3cf/fast] Error 2
gmake[1]: Leaving directory `/usr/lfs/hdd_v1/rc-buildroot-test/scripts/instance-1/output-1/build/bullet-3.09/CMakeFiles/CMakeTmp'