-Wdeprecated: Use noexcept rather than throw() where supported

Summary: I've copy/pasted the LLVM_NOEXCEPT definition macro goo from LLVM's Compiler.h. Is there somewhere I should put this in Compiler RT? Is there a useful header to define/share things like this?

Reviewers: samsonov

Differential Revision: http://reviews.llvm.org/D11780

llvm-svn: 244453