[lld-macho] Implement -force_load_swift_libs

It causes libraries whose names start with "swift" to be force-loaded.
Note that unlike the more general `-force_load`, this flag only applies
to libraries specified via LC_LINKER_OPTIONS, and not those passed on
the command-line. This is what ld64 does.

Reviewed By: #lld-macho, thakis

Differential Revision: https://reviews.llvm.org/D103709