GEH: Make each element of the deprecation macros overridable.

This way, we can override only FOO_DEPRECATED to silence deprecation
for a library.

Modules/exportheader.cmake.in

@@ -23,7 +23,13 @@
 
 #ifndef @DEPRECATED_MACRO_NAME@
 #  define @DEPRECATED_MACRO_NAME@ @DEFINE_DEPRECATED@
+#endif
+
+#ifndef @DEPRECATED_MACRO_NAME@_EXPORT
 #  define @DEPRECATED_MACRO_NAME@_EXPORT @EXPORT_MACRO_NAME@ @DEPRECATED_MACRO_NAME@
+#endif
+
+#ifndef @DEPRECATED_MACRO_NAME@_NO_EXPORT
 #  define @DEPRECATED_MACRO_NAME@_NO_EXPORT @NO_EXPORT_MACRO_NAME@ @DEPRECATED_MACRO_NAME@
 #endif