[clang] Fix format test 
[clang] Fix format test 

This diff makes the test FixIt/format.m more robust.
The issue was caught by the build bot clang-cmake-thumbv7-a15.

Test plan: make check-all


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@308073 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang