Skip 'really hidden' options when performing lookup of the nearest
option when invalid option was passed. Since these options aren't even
documented in --help-hidden, it seems inconsistent to suggest them
to users.
This fixes clang-tools-extra test failures due to unexpected suggestions
when linking the tools to LLVM dylib (that provides more options than
the subset of LLVM libraries linked directly).
Differential Revision: https://reviews.llvm.org/D82001
6b982af8c2