[Clang] Fix unknown type attributes diagnosed twice with [[]] spelling

Don't warn on unknown type attributes in Parser::ProhibitCXX11Attributes
for most cases, but left the diagnostic to the later checks.
module declaration and module import declaration are special cases.

Fixes https://github.com/llvm/llvm-project/issues/54817

Differential Revision: https://reviews.llvm.org/D123447