[LLD] [COFF] Prefer paths specified with -libpath: over toolchain paths (#78039)

The main reason for adding the toolchain paths early was to prefer
libraries from the toolchain over ones from MSVC (primarily for
compiler-rt builtins). But if the user specifies a directory explicitly
with the -libpath: option, that should be preferred over the built-in
default paths.

This fixes an issue raised at
https://discourse.llvm.org/t/lld-prefers-system-llvm-libraries-to-user-provided-ones-on-windows/76148.