As we have --std=c99 in CMAKE_C_FLAGS, to expose some macros and functions we should declare feature-check-marco...
Define _DARWIN_C_SOURCE should enable all mac os non standard extensions.
Merge branch 'cmake-try-fix-luasocket-build' into check-test-jenkins

* cmake-try-fix-luasocket-build:
  As we have --std=c99 in CMAKE_C_FLAGS, to expose some macros and functions we should declare feature-check-marco... Define _DARWIN_C_SOURCE should enable all mac os non standard extensions.