Add -Wvarargs option

Several warnings related to questionable usage cases of variadic
function related macros (like va_start) could not be controlled by any
warning-related macro.  Fixed thus, by introducing the -Wvarargs
option.

Tested on x86_64-unknown-linux-gnu against trunk.

gcc/c-family/

	* c.opt (Wvarargs):  Define new option.

gcc/
	* builtins.c (fold_builtin_next_arg):  Use OPT_Wvarargs as an
	argument for the various warning_at calls.

gcc/doc/

	* invoke.texi: Update the documentation.

gcc/testsuite/

	* c-c++-common/Wvarargs.c: New test case.
	* c-c++-common/Wvarargs-2.c: Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@186978 138bc75d-0d04-0410-961f-82ee72b054a4

1 files changed, 4 insertions, 4 deletions

diff --git a/gcc/builtins.c b/gcc/builtins.c
index 5ddc47bd7ea..41a052b1d8f 100644
--- a/gcc/builtins.c
+++ b/gcc/builtins.c
@@ -12127,8 +12127,8 @@ fold_builtin_next_arg (tree exp, bool va_start_p)
 	  /* Evidently an out of date version of <stdarg.h>; can't validate
 	     va_start's second argument, but can still work as intended.  */
 	  warning_at (current_location,
-		      0,
-		      "%<__builtin_next_arg%> called without an argument");
+		      OPT_Wvarargs,
+		   "%<__builtin_next_arg%> called without an argument");
 	  return true;
 	}
       else if (nargs > 1)
@@ -12164,7 +12164,7 @@ fold_builtin_next_arg (tree exp, bool va_start_p)
 	     argument so that we will get wrong-code because of
 	     it.  */
 	  warning_at (current_location,
-		      0,
+		      OPT_Wvarargs,
 		      "second parameter of %<va_start%> not last named argument");
 	}
 
@@ -12177,7 +12177,7 @@ fold_builtin_next_arg (tree exp, bool va_start_p)
       else if (DECL_REGISTER (arg))
 	{
 	  warning_at (current_location,
-		      0,
+		      OPT_Wvarargs,
 		      "undefined behaviour when second parameter of "
 		      "%<va_start%> is declared with %<register%> storage");
 	}