Source/Modules/OverrideC.cmake - third_party/github.com/Kitware/CMake - Git at Google

 if("${CMAKE_SYSTEM_NAME};${CMAKE_C_COMPILER_ID}" STREQUAL "AIX;GNU")
   string(APPEND CMAKE_C_FLAGS_INIT " -pthread")
 endif()
	if("${CMAKE_SYSTEM_NAME};${CMAKE_C_COMPILER_ID}" STREQUAL "AIX;GNU")
	string(APPEND CMAKE_C_FLAGS_INIT " -pthread")
	endif()