This diagnostic did not accept arguments, and did not have any test coverage. Parameterized the diagnostic, and made it more consistent with other attribute diagnostic wordings. Added test coverage.

Since this warning was generalized, it was also given a sensible warning group flag and the corresponding test was updated to reflect this.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198053 91177308-0d34-0410-b5e6-96231b3b80d8