Add a test that checks that the formatter doesn't discard '@' with ObjC1 set.

Also set ObjC1 in the formatter tests.

The only effect of this flag in the lexer is that '@' now gets turned into
tok::at instead of tok::unknown.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171742 91177308-0d34-0410-b5e6-96231b3b80d8