Move checkStringLiteralArgument into Sema class

It's a useful function to have around for target-specific attributes.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191768 91177308-0d34-0410-b5e6-96231b3b80d8
Implement ARM GNU-style interrupt attribute

This attribute allows users to use a modified C or C++ function as an ARM
exception-handling function and, with care, to successfully return control to
user-space after the issue has been dealt with.

rdar://problem/14207019

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@191769 91177308-0d34-0410-b5e6-96231b3b80d8