[lld-macho] Implement -hidden-l

Similarly to -load_hidden, this flag instructs the linker to not export
symbols from the specified archive. While that flag takes a path,
-hidden-l looks for the specified library name in the search path.

The test changes are needed because -hidden-lfoo resolves to libfoo.a,
not foo.a.

Differential Revision: https://reviews.llvm.org/D130529