Fix ClangFormat issue of recognizing ObjC subscript as C++ attributes when...

Fix ClangFormat issue of recognizing ObjC subscript as C++ attributes when message target is a result of a C-style method.

Summary:
The issue is that for array subscript like:

```
arr[[Foo() bar]];
```
ClangFormat will recognize it as C++11 attribute syntax and put a space between 'arr' and first '[', like:

```
arr [[Foo() bar]];
```

Now it is fixed. Tested with:
```
ninja FormatTests
```

Reviewers: benhamilton

Reviewed By: benhamilton

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D54288

llvm-svn: 346566