Rename subsystem_DEPRECATED to subsystem_DEPRECATED_FUNCTION(X)

Start to explain what the replacement function is.
Generate the #define/#undef logic in generated header files.
Use gcc style where the deprecation warning is after the prototype.

lib/krb5/mit_glue.c

@@ -31,8 +31,6 @@
  * SUCH DAMAGE.
  */
 
-#define KRB5_DEPRECATED
-
 #include "krb5_locl.h"
 
 #ifndef HEIMDAL_SMALLER
@@ -316,12 +314,12 @@ krb5_c_encrypt_length(krb5_context context,
  * @ingroup krb5_deprecated
  */
 
-KRB5_DEPRECATED
 KRB5_LIB_FUNCTION krb5_error_code KRB5_LIB_CALL
 krb5_c_enctype_compare(krb5_context context,
 		       krb5_enctype e1,
 		       krb5_enctype e2,
 		       krb5_boolean *similar)
+    KRB5_DEPRECATED_FUNCTION("Use X instead")
 {
     *similar = (e1 == e2);
     return 0;