R600: Cleanup fadd and fsub tests

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214991 91177308-0d34-0410-b5e6-96231b3b80d8
Fix a test that has no checks.

X86 doesn't have fneg, so check for xor.

Differential Revision: http://reviews.llvm.org/D4812


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214992 91177308-0d34-0410-b5e6-96231b3b80d8