Determining if the pthread_create exist failed with the following output:
Change Dir: /var/tmp/portage/app-admin/conky-1.10.0/work/conky-1.10.0_build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/ninja" "cmTC_f35d2"
[1/2] Building C object CMakeFiles/cmTC_f35d2.dir/CheckSymbolExists.c.o
[2/2] Linking C executable cmTC_f35d2
FAILED: : && /usr/bin/x86_64-pc-linux-gnu-gcc  -march=native -O2 -pipe  -Wl,-O1 -Wl,--as-needed CMakeFiles/cmTC_f35d2.dir/CheckSymbolExists.c.o  -o cmTC_f35d2  -rdynamic && :
CMakeFiles/cmTC_f35d2.dir/CheckSymbolExists.c.o: In function `main':
CheckSymbolExists.c:(.text.startup+0x6): undefined reference to `pthread_create'
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.

File /var/tmp/portage/app-admin/conky-1.10.0/work/conky-1.10.0_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 the function pthread_create exists in the pthreads failed with the following output:
Change Dir: /var/tmp/portage/app-admin/conky-1.10.0/work/conky-1.10.0_build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/ninja" "cmTC_aae62"
[1/2] Building C object CMakeFiles/cmTC_aae62.dir/CheckFunctionExists.c.o
[2/2] Linking C executable cmTC_aae62
FAILED: : && /usr/bin/x86_64-pc-linux-gnu-gcc  -march=native -O2 -pipe  -DCHECK_FUNCTION_EXISTS=pthread_create  -Wl,-O1 -Wl,--as-needed CMakeFiles/cmTC_aae62.dir/CheckFunctionExists.c.o  -o cmTC_aae62  -rdynamic -lpthreads && :
/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lpthreads
collect2: error: ld returned 1 exit status
ninja: build stopped: subcommand failed.


Determining if the pipe2 exist failed with the following output:
Change Dir: /var/tmp/portage/app-admin/conky-1.10.0/work/conky-1.10.0_build/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/ninja" "cmTC_287ae"
[1/2] Building C object CMakeFiles/cmTC_287ae.dir/CheckSymbolExists.c.o
FAILED: /usr/bin/x86_64-pc-linux-gnu-gcc  -D_LARGEFILE64_SOURCE -D_POSIX_C_SOURCE=200809L  -DNDEBUG -std=c99 -o CMakeFiles/cmTC_287ae.dir/CheckSymbolExists.c.o -c CheckSymbolExists.c
CheckSymbolExists.c: In function ‘main’:
CheckSymbolExists.c:8:19: error: ‘pipe2’ undeclared (first use in this function)
   return ((int*)(&pipe2))[argc];
                   ^
CheckSymbolExists.c:8:19: note: each undeclared identifier is reported only once for each function it appears in
ninja: build stopped: subcommand failed.

File /var/tmp/portage/app-admin/conky-1.10.0/work/conky-1.10.0_build/CMakeFiles/CMakeTmp/CheckSymbolExists.c:
/* */
#include <unistd.h>

int main(int argc, char** argv)
{
  (void)argv;
#ifndef pipe2
  return ((int*)(&pipe2))[argc];
#else
  (void)argc;
  return 0;
#endif
}