[hexagon] restore library path arguments

Before applying this fix, clang would not include the specified library
path arguments:

    $ ./bin/clang --target=hexagon-unknown-linux-musl  -o tprog tprog.o -L/tmp -###
    ...
    clang: warning: argument unused during compilation: '-L/tmp' [-Wunused-command-line-argument]
     "/local/mnt/workspace/install/clang-latest/bin/ld.lld" "-z" "relro" "-o" "tprog" "-dynamic-linker=/lib/ld-musl-hexagon.so.1" "/usr/lib/crt1.o" "-L/usr/lib" "tprog.o" "-lclang_rt.builtins-hexagon" "-lc"

Differential Revision: https://reviews.llvm.org/D156330