system: Add WARN_UNUSED_RESULT

I'd like to have the option of marking functions with
__attribute__ ((__warn_unused_result__)), so this patch adds a macro.
And use it for maybe_wrap_with_location, it's always a bug if the
return value is not used, which happened to me and got me confused.

gcc/ChangeLog:

	* system.h (WARN_UNUSED_RESULT): Define for GCC >= 3.4.
	* tree.h (maybe_wrap_with_location): Add WARN_UNUSED_RESULT.

1 files changed, 1 insertions, 1 deletions

diff --git a/gcc/tree.h b/gcc/tree.h
index 684be10..9a713cd 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -1214,7 +1214,7 @@ get_expr_source_range (tree expr)
 extern void protected_set_expr_location (tree, location_t);
 extern void protected_set_expr_location_if_unset (tree, location_t);
 
-extern tree maybe_wrap_with_location (tree, location_t);
+WARN_UNUSED_RESULT extern tree maybe_wrap_with_location (tree, location_t);
 
 extern int suppress_location_wrappers;