Determining if the pthread_create exist failed with the following output:
Change Dir: /home/buildroot/buildroot-test/instance-1/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_6c94a/fast"
make[1]: Entering directory `/home/buildroot/buildroot-test/instance-1/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_6c94a.dir/build.make CMakeFiles/cmTC_6c94a.dir/build
make[2]: Entering directory `/home/buildroot/buildroot-test/instance-1/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_6c94a.dir/CheckSymbolExists.c.o
/home/buildroot/buildroot-test/instance-1/output/host/bin/arc-buildroot-linux-gnu-gcc --sysroot=/home/buildroot/buildroot-test/instance-1/output/host/arc-buildroot-linux-gnu/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -matomic -Os   -DNDEBUG   -o CMakeFiles/cmTC_6c94a.dir/CheckSymbolExists.c.o   -c /home/buildroot/buildroot-test/instance-1/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp/CheckSymbolExists.c
Linking C executable cmTC_6c94a
/home/buildroot/buildroot-test/instance-1/output/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_6c94a.dir/link.txt --verbose=1
/home/buildroot/buildroot-test/instance-1/output/host/bin/arc-buildroot-linux-gnu-gcc --sysroot=/home/buildroot/buildroot-test/instance-1/output/host/arc-buildroot-linux-gnu/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -matomic -Os   -DNDEBUG    -rdynamic CMakeFiles/cmTC_6c94a.dir/CheckSymbolExists.c.o  -o cmTC_6c94a 
/home/buildroot/buildroot-test/instance-1/output/host/lib/gcc/arc-buildroot-linux-gnu/8.2.1/../../../../arc-buildroot-linux-gnu/bin/ld: CMakeFiles/cmTC_6c94a.dir/CheckSymbolExists.c.o: in function `main':
CheckSymbolExists.c:(.text.startup+0x4): undefined reference to `pthread_create'
/home/buildroot/buildroot-test/instance-1/output/host/lib/gcc/arc-buildroot-linux-gnu/8.2.1/../../../../arc-buildroot-linux-gnu/bin/ld: CheckSymbolExists.c:(.text.startup+0x4): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
make[2]: *** [cmTC_6c94a] Error 1
make[2]: Leaving directory `/home/buildroot/buildroot-test/instance-1/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
make[1]: *** [cmTC_6c94a/fast] Error 2
make[1]: Leaving directory `/home/buildroot/buildroot-test/instance-1/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'

File /home/buildroot/buildroot-test/instance-1/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: /home/buildroot/buildroot-test/instance-1/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_bfaff/fast"
make[1]: Entering directory `/home/buildroot/buildroot-test/instance-1/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_bfaff.dir/build.make CMakeFiles/cmTC_bfaff.dir/build
make[2]: Entering directory `/home/buildroot/buildroot-test/instance-1/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
Building C object CMakeFiles/cmTC_bfaff.dir/CheckForPthreads.c.o
/home/buildroot/buildroot-test/instance-1/output/host/bin/arc-buildroot-linux-gnu-gcc --sysroot=/home/buildroot/buildroot-test/instance-1/output/host/arc-buildroot-linux-gnu/sysroot   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -matomic -Os   -DNDEBUG   -o CMakeFiles/cmTC_bfaff.dir/CheckForPthreads.c.o   -c /home/buildroot/buildroot-test/instance-1/output/host/share/cmake-3.8/Modules/CheckForPthreads.c
Linking C executable cmTC_bfaff
/home/buildroot/buildroot-test/instance-1/output/host/bin/cmake -E cmake_link_script CMakeFiles/cmTC_bfaff.dir/link.txt --verbose=1
/home/buildroot/buildroot-test/instance-1/output/host/bin/arc-buildroot-linux-gnu-gcc --sysroot=/home/buildroot/buildroot-test/instance-1/output/host/arc-buildroot-linux-gnu/sysroot -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -matomic -Os   -DNDEBUG    -rdynamic CMakeFiles/cmTC_bfaff.dir/CheckForPthreads.c.o  -o cmTC_bfaff -pthread 
make[2]: Leaving directory `/home/buildroot/buildroot-test/instance-1/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'
make[1]: Leaving directory `/home/buildroot/buildroot-test/instance-1/output/build/i2pd-2.22.0/build/CMakeFiles/CMakeTmp'