clang-format: Improve formatting of ObjC Blocks with return type.

Before:
  int a = [operation block:^int(int * i) { return 1; }];

After:
  int a = [operation block:^int(int *i) { return 1; }];

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199411 91177308-0d34-0410-b5e6-96231b3b80d8