[PATCH] Implement nonnull-attribute sanitizer

[Richard Smith]

Yes, I think it makes sense for returns_nonnull too.

================
Comment at: projects/compiler-rt/lib/ubsan/ubsan_handlers.h:135
@@ +134,3 @@
+  SourceLocation Loc;
+  SourceLocation DeclLoc;
+  int ArgIndex;
----------------
Maybe AttrLoc?

http://reviews.llvm.org/D5082