[lld][COFF] Add -print-search-paths for debugging.

While working on adding more implicit search paths to the
lld COFF driver, it was helpful to have a way to print all
the search paths, both for debugging and for testing without
having to create very complicated test cases.

This is a simple arg that just prints the search paths and exits.

Related to the efforts in #63827

Differential Revision: https://reviews.llvm.org/D155047