Determining if the getpassphrase exist failed with the following output:
Change Dir: /data/buildroot/buildroot-test/instance-0/output/build/znc-1.7.5/CMakeFiles/CMakeTmp

Run Build Command:"/usr/bin/make" "cmTC_d1aa4/fast"
make[1]: Entering directory '/data/buildroot/buildroot-test/instance-0/output/build/znc-1.7.5/CMakeFiles/CMakeTmp'
/usr/bin/make -f CMakeFiles/cmTC_d1aa4.dir/build.make CMakeFiles/cmTC_d1aa4.dir/build
make[2]: Entering directory '/data/buildroot/buildroot-test/instance-0/output/build/znc-1.7.5/CMakeFiles/CMakeTmp'
Building CXX object CMakeFiles/cmTC_d1aa4.dir/CheckSymbolExists.cxx.o
/data/buildroot/buildroot-test/instance-0/output/host/bin/arm-linux-g++ --sysroot=/data/buildroot/buildroot-test/instance-0/output/host/arm-buildroot-linux-musleabihf/sysroot    -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -Os   -DNDEBUG   -o CMakeFiles/cmTC_d1aa4.dir/CheckSymbolExists.cxx.o -c /data/buildroot/buildroot-test/instance-0/output/build/znc-1.7.5/CMakeFiles/CMakeTmp/CheckSymbolExists.cxx
/data/buildroot/buildroot-test/instance-0/output/build/znc-1.7.5/CMakeFiles/CMakeTmp/CheckSymbolExists.cxx: In function 'int main(int, char**)':
/data/buildroot/buildroot-test/instance-0/output/build/znc-1.7.5/CMakeFiles/CMakeTmp/CheckSymbolExists.cxx:8:19: error: 'getpassphrase' was not declared in this scope
   return ((int*)(&getpassphrase))[argc];
                   ^~~~~~~~~~~~~
make[2]: *** [CMakeFiles/cmTC_d1aa4.dir/build.make:66: CMakeFiles/cmTC_d1aa4.dir/CheckSymbolExists.cxx.o] Error 1
make[2]: Leaving directory '/data/buildroot/buildroot-test/instance-0/output/build/znc-1.7.5/CMakeFiles/CMakeTmp'
make[1]: *** [Makefile:126: cmTC_d1aa4/fast] Error 2
make[1]: Leaving directory '/data/buildroot/buildroot-test/instance-0/output/build/znc-1.7.5/CMakeFiles/CMakeTmp'

File /data/buildroot/buildroot-test/instance-0/output/build/znc-1.7.5/CMakeFiles/CMakeTmp/CheckSymbolExists.cxx:
/* */
#include <stdlib.h>

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