cmake HAVE_CLOCK examples

SWI-Prolog/swipl-devel cmake/Config.cmake :262 

check_function_exists(clock HAVE_CLOCK)

gccxml/gccxml GCC/config_cmake/CMakeLists.txt :213 

CHECK_FUNCTION_EXISTS(clock HAVE_CLOCK)

gccxml/gccxml GCC/config_cmake/CMakeLists.txt :474 

CHECK_FUNCTION_EXISTS(clock HAVE_CLOCK)