Determining if the pthread_create exist failed with the following output:
Change Dir: /usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/gmake" "cmTC_2e5a4/fast"
gmake[1]: Entering directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
/usr/bin/gmake -f CMakeFiles/cmTC_2e5a4.dir/build.make CMakeFiles/cmTC_2e5a4.dir/build
gmake[2]: Entering directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_2e5a4.dir/CheckSymbolExists.c.o
/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/host/arm-buildroot-linux-gnueabi/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os   -DNDEBUG   -o CMakeFiles/cmTC_2e5a4.dir/CheckSymbolExists.c.o   -c /usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_2e5a4
/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_2e5a4.dir/link.txt --verbose=1
/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/host/arm-buildroot-linux-gnueabi/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os   -DNDEBUG    -rdynamic CMakeFiles/cmTC_2e5a4.dir/CheckSymbolExists.c.o  -o cmTC_2e5a4 
CMakeFiles/cmTC_2e5a4.dir/CheckSymbolExists.c.o: In function `main':
CheckSymbolExists.c:(.text.startup+0x8): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
gmake[2]: *** [cmTC_2e5a4] Error 1
gmake[2]: Leaving directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
gmake[1]: *** [cmTC_2e5a4/fast] Error 2
gmake[1]: Leaving directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'

File /usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include <pthread.h>

int main(int argc, char** argv)
{
  (void)argv;
#ifndef pthread_create
  return ((int*)(&pthread_create))[argc];
#else
  (void)argc;
  return 0;
#endif
}

Determining if compiler accepts -pthread returned OFF instead of 2. The compiler had the following output:
Change Dir: /usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/gmake" "cmTC_d1289/fast"
gmake[1]: Entering directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
/usr/bin/gmake -f CMakeFiles/cmTC_d1289.dir/build.make CMakeFiles/cmTC_d1289.dir/build
gmake[2]: Entering directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_d1289.dir/CheckForPthreads.c.o
/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/host/arm-buildroot-linux-gnueabi/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os   -DNDEBUG   -o CMakeFiles/cmTC_d1289.dir/CheckForPthreads.c.o   -c /usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/host/share/cmake-3.8/Modules/CheckForPthreads.c
Linking C executable cmTC_d1289
/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_d1289.dir/link.txt --verbose=1
/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/host/bin/arm-none-linux-gnueabi-gcc --sysroot=/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/host/arm-buildroot-linux-gnueabi/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os   -DNDEBUG    -rdynamic CMakeFiles/cmTC_d1289.dir/CheckForPthreads.c.o  -o cmTC_d1289 -pthread 
gmake[2]: Leaving directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
gmake[1]: Leaving directory `/usr/lfs/v0/rc-buildroot-test/scripts/instance-0/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'