PR9547: If we're parsing a simple-declaration that contains a tag definition,

PR9547: If we're parsing a simple-declaration that contains a tag definition,
and we see an ill-formed declarator that would probably be well-formed if the
tag definition were just missing a semicolon, use that as the diagnostic
instead of producing some other mysterious error.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@195163 91177308-0d34-0410-b5e6-96231b3b80d8