GetPrerequisites: Add deprecation notice

GetPrerequisites has now been superceded by file(GET_RUNTIME_DEPENDENCIES),
so add a deprecation notice stating such.

Help/release/dev/get-runtime-dependencies.rst

@@ -5,3 +5,5 @@ get-runtime-dependencies
   ``GET_RUNTIME_DEPENDENCIES``, which allows you to recursively get the list of
   libraries linked by an executable or library. This sub-command is intended as
   a replacement for :module:`GetPrerequisites`.
+* The :module:`GetPrerequisites` module has been deprecated, as it has been
+  superceded by :command:`file(GET_RUNTIME_DEPENDENCIES)`.

Modules/GetPrerequisites.cmake

@@ -5,6 +5,10 @@
 GetPrerequisites
 ----------------
 
+.. deprecated:: 3.16
+
+  Use :command:`file(GET_RUNTIME_DEPENDENCIES)` instead.
+
 Functions to analyze and list executable file prerequisites.
 
 This module provides functions to list the .dll, .dylib or .so files