clang-check: rename the local FixItAction
clang-check: rename the local FixItAction

Resolve the ambiguity in the FixItAction definition by renaming the type.  With
Xcode 9.2, you would fail to build this with:

  llvm/tools/clang/tools/clang-check/ClangCheck.cpp:183:48: error: reference to 'FixItAction' is ambiguous
      FrontendFactory = newFrontendActionFactory<FixItAction>();
                                                 ^

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@341877 91177308-0d34-0410-b5e6-96231b3b80d8

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