cmake: Add FindClockGettime module

Author: hebasto

cmake/FindClockGettime.cmake

@@ -0,0 +1,47 @@
+#[=======================================================================[
+FindClockGettime
+----------------
+
+Finds the clock_gettime() POSIX function on the system.
+
+Imported Targets
+^^^^^^^^^^^^^^^^
+
+This module provides the following Imported Targets:
+
+POSIX::clock_gettime
+  Target encapsulating the clock_gettime() usage requirements, available
+  only if clock_gettime() is found.
+
+#]=======================================================================]
+
+include(CheckSymbolExists)
+include(CMakePushCheckState)
+
+cmake_push_check_state(RESET)
+
+set(CMAKE_REQUIRED_DEFINITIONS -D_POSIX_C_SOURCE=199309L)
+check_symbol_exists(clock_gettime "time.h" CLOCK_GETTIME_IS_BUILT_IN)
+set(${CMAKE_FIND_PACKAGE_NAME}_FOUND ${CLOCK_GETTIME_IS_BUILT_IN})
+
+if(NOT ${CMAKE_FIND_PACKAGE_NAME}_FOUND)
+  set(CMAKE_REQUIRED_LIBRARIES rt)
+  check_symbol_exists(clock_gettime "time.h" CLOCK_GETTIME_NEEDS_LINK_TO_LIBRT)
+  set(${CMAKE_FIND_PACKAGE_NAME}_FOUND ${CLOCK_GETTIME_NEEDS_LINK_TO_LIBRT})
+endif()
+
+if(${CMAKE_FIND_PACKAGE_NAME}_FOUND)
+  if(NOT TARGET POSIX::clock_gettime)
+    add_library(POSIX::clock_gettime INTERFACE IMPORTED)
+    set_target_properties(POSIX::clock_gettime PROPERTIES
+      INTERFACE_COMPILE_DEFINITIONS "${CMAKE_REQUIRED_DEFINITIONS}"
+      INTERFACE_LINK_LIBRARIES "${CMAKE_REQUIRED_LIBRARIES}"
+    )
+  endif()
+else()
+  if(${CMAKE_FIND_PACKAGE_NAME}_FIND_REQUIRED)
+    message(FATAL_ERROR "clock_gettime() not available.")
+  endif()
+endif()
+
+cmake_pop_check_state()