clang: disable documentation-deprecated-sync

Add the `-Wno-documentation-deprecated-sync` switch when compiling with
clang, since our documentation adds `deprecated` markers, but we do not
add the deprecation attribute in the code itself.  (ie, the code is out
of sync with the docs).

In fact, we do not _want_ to mark these items as deprecated in the code,
at least not yet, as we are not quite ready to bother our end-users with
this since they're not going away.

CMakeLists.txt

@@ -252,6 +252,10 @@ ELSE ()
 		ENABLE_WARNINGS(format-security)
 	ENDIF()
 
+	IF("${CMAKE_C_COMPILER_ID}" STREQUAL "Clang")
+		DISABLE_WARNINGS(documentation-deprecated-sync)
+	ENDIF()
+
 	IF (PROFILE)
 		SET(CMAKE_C_FLAGS "-pg ${CMAKE_C_FLAGS}")
 		SET(CMAKE_EXE_LINKER_FLAGS "-pg ${CMAKE_EXE_LINKER_FLAGS}")