OSX 10.11 does not have clock_gettime() clang <= 8.0.0 has a bug in __builtin_cpu_supports() and it doesn't function. see https://llvm.org/bugs/show_bug.cgi?id=25510
* Fix compile errors with MacOS - _POSIX_C_SOURCE must not be defined for num_CPU() * separate util_posix.c require changes in tools directory as well * remove unnecessary self-include