Source: Suppress some warnings on LCC 1.23.x

LCC 1.23.x (confirmed for 1.23.10, 1.23.19, maybe others)
issues -Wunused-function warning on the following functions:
Source/cmFileAPICodemodel.cxx:126, ValueEq()
Source/cmFileAPICodemodel.cxx:130, ValueLess()
Source/cmGeneratorExpressionNode.cxx:630, back()
This fix makes it silent for compatibility.
This is not a subject for newer LCC versions, like 1.25 and 1.26.
On LCC 1.21 CMake is not buildable, and 1.22 and 1.24 are not
tested, as they are internal development versions. Thus, the fix
is only applied if LCC 1.23 is detected.

Source/cmConfigure.cmake.h.in

@@ -14,6 +14,10 @@
 #pragma warning(disable : 1572) /* floating-point equality test */
 #endif
 
+#if defined(__LCC__) && defined(__EDG__) && (__LCC__ == 123)
+#pragma diag_suppress 2910 /* excess -Wunused-function in 1.23.x */
+#endif
+
 #cmakedefine HAVE_ENVIRON_NOT_REQUIRE_PROTOTYPE
 #cmakedefine HAVE_UNSETENV
 #cmakedefine CMake_USE_MACH_PARSER