[clang] Avoid suggesting typoed directives in `.S` files

This patch is itended to avoid suggesting typoed directives in `.S`
files to support the cases of `#` directives treated as comments or
various pseudo-ops. The feature is implemented in
https://reviews.llvm.org/D124726.

Fixes: https://reviews.llvm.org/D124726#3516346.

Reviewed By: nickdesaulniers

Differential Revision: https://reviews.llvm.org/D125727