Move x86-specific bits of warn-unused-local-typedef.cpp into their own file.

That way, most of the test can run everywhere. Also give the new file an x86
triple in addition to a REQUIRES line.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@217314 91177308-0d34-0410-b5e6-96231b3b80d8