CMakeDetermineVSServicePack: Add deprecation diagnostic

Warn project developers at runtime that the module should not be used
anymore.  Issue the diagnostic only when the project requires a new
enough CMake to use the alternative.  Honor the
CMAKE_(ERROR|WARN)_DEPRECATED settings.

Help/release/dev/CMakeDetermineVSServicePack.rst

@@ -0,0 +1,6 @@
+CMakeDetermineVSServicePack
+---------------------------
+
+* The :module:`CMakeDetermineVSServicePack` module now warns that
+  it is deprecated and should not longer be used.  Use the
+  :variable:`CMAKE_<LANG>_COMPILER_VERSION` variable instead.

Modules/CMakeDetermineVSServicePack.cmake

@@ -43,6 +43,13 @@
 # (To distribute this file outside of CMake, substitute the full
 #  License text for the above reference.)
 
+if(NOT CMAKE_MINIMUM_REQUIRED_VERSION VERSION_LESS 2.8.8)
+  message(DEPRECATION
+    "This module is deprecated and should not be used.  "
+    "Use the CMAKE_<LANG>_COMPILER_VERSION variable instead."
+    )
+endif()
+
 # [INTERNAL]
 # Please do not call this function directly
 function(_DetermineVSServicePackFromCompiler _OUT_VAR _cl_version)