[C PATCH] Fix -Wbuiltin-declaration-mismatch (PR c/89525)

[Jakub Jelinek]

Hi!

As the following testcase shows, with -w we don't emit
-Wbuiltin-declaration-mismatch warnings (correct), but emit weird messages:
~/src/gcc/obj46/gcc/xgcc -B ~/src/gcc/obj46/gcc/ -w pr89525.c  -S
pr89525.c: In function ‘foo’:
pr89525.c:5:8: note: declared here
    5 | double sqrt (); /* { dg-bogus "declared here" } */
      |        ^~~~

Fixed thusly, bootstrapped/regtested on x86_64-linux and i686-linux, ok for
trunk?

2019-02-27  Jakub Jelinek  <jakub@redhat.com>

	PR c/89525
	* c-typeck.c (convert_arguments): Call inform_declaration only if
	the previous warning_at call returned true.

	* gcc.dg/pr89525.c: New test.

--- gcc/c/c-typeck.c.jj	2019-01-24 20:15:16.913439861 +0100
+++ gcc/c/c-typeck.c	2019-02-27 21:33:37.815873072 +0100
@@ -3509,12 +3509,10 @@ convert_arguments (location_t loc, vec<l
 
       if (builtin_type == void_type_node)
 	{
-	  warning_at (loc, OPT_Wbuiltin_declaration_mismatch,
-		      "too many arguments to built-in function %qE "
-		      "expecting %d",
-		      function, parmnum);
-
-	  inform_declaration (fundecl);
+	  if (warning_at (loc, OPT_Wbuiltin_declaration_mismatch,
+			  "too many arguments to built-in function %qE "
+			  "expecting %d", function, parmnum))
+	    inform_declaration (fundecl);
 	  builtin_typetail = NULL_TREE;
 	}
 
@@ -3651,10 +3649,10 @@ convert_arguments (location_t loc, vec<l
       for (tree t = builtin_typetail; t; t = TREE_CHAIN (t))
 	++nargs;
 
-      warning_at (loc, OPT_Wbuiltin_declaration_mismatch,
-		  "too few arguments to built-in function %qE expecting %u",
-		  function, nargs - 1);
-      inform_declaration (fundecl);
+      if (warning_at (loc, OPT_Wbuiltin_declaration_mismatch,
+		      "too few arguments to built-in function %qE "
+		      "expecting %u", function, nargs - 1))
+	inform_declaration (fundecl);
     }
 
   return error_args ? -1 : (int) parmnum;
--- gcc/testsuite/gcc.dg/pr89525.c.jj	2019-02-27 21:34:45.863757616 +0100
+++ gcc/testsuite/gcc.dg/pr89525.c	2019-02-27 21:34:24.232112209 +0100
@@ -0,0 +1,11 @@
+/* PR c/89525 */
+/* { dg-do compile } */
+/* { dg-options "-w" } */
+
+double sqrt ();	/* { dg-bogus "declared here" } */
+
+void
+foo (void)
+{
+  sqrt ();
+}

	Jakub