Combine identical check-prefixes in Clang test/Preprocessor/arm-target-features.c

Reviewers: rengolin, t.p.northover

Subscribers: aemerson, cfe-commits, rengolin

Differential Revision: http://reviews.llvm.org/D18391

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@264155 91177308-0d34-0410-b5e6-96231b3b80d8