Test for warning being silenced

Summary:
Added some tests to see if the new warning would be silenced with a flag.

Patch by Arthur Marble <arthur@info9.net> in the context of Debian Google Summer of code 2014.


Reviewers: sylvestre.ledru

Reviewed By: sylvestre.ledru

Differential Revision: http://reviews.llvm.org/D4475

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212833 91177308-0d34-0410-b5e6-96231b3b80d8
Add nonnull in CodeGen for __attribute__((nonnull))

We now have an LLVM-level nonnull attribute that can be applied to function
parameters, and we emit it for reference types (as of r209723), but did not
emit it when an __attribute__((nonnull)) was provided. Now we will.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@212835 91177308-0d34-0410-b5e6-96231b3b80d8