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: http://llvm.org/svn/llvm-project/cfe/trunk@198053 91177308-0d34-0410-b5e6-96231b3b80d8
Removed a string literal for an attribute name, which means the attribute name will be quoted in the diagnostic. Manually added some quotes to a diagnostic for consistency. Updated the test cases as appropriate.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@198054 91177308-0d34-0410-b5e6-96231b3b80d8