[patch, fortran] PR 122245: Fix -fc-prototypes when procedure is defined via INTERFACE

[Thomas Koenig]

Hello world,

what it says in the ChangeLog.  No test case, see PR 120220. Thanks
to Harald for spotting this.

Regression-tested. OK for trunk?

Best regards

        Thomas

PR 122245: Fix -fc-prototypes when procedure is defined via INTERFACE

This simple patch emits correct prototypes when a procedure is
defined via an interface by simply checking the presence
of an interface and using its formal arglist.

gcc/fortran/ChangeLog:

        PR fortran/122245
        * dump-parse-tree.cc (write_formal_arglist): Take the formal
        arglist from the symbol's interface if it is present.
diff --git a/gcc/fortran/dump-parse-tree.cc b/gcc/fortran/dump-parse-tree.cc
index 028c946d2d9..1b3c587179c 100644
--- a/gcc/fortran/dump-parse-tree.cc
+++ b/gcc/fortran/dump-parse-tree.cc
@@ -4513,7 +4513,12 @@ write_formal_arglist (gfc_symbol *sym, bool bind_c)
 {
   gfc_formal_arglist *f;
 
-  for (f = sym->formal; f != NULL; f = f->next)
+  if (sym->ts.interface)
+    f = sym->ts.interface->formal;
+  else
+    f = sym->formal;
+
+  for (; f != NULL; f = f->next)
     {
       enum type_return rok;
       const char *intent_in;