Do not prepend target triple to -fuse-ld=lld,mold.
lld and mold are platform-agnostic and not prefixed with target triple.
Prepending the target triple makes it less likely to find the intended
linker executable.
A potential breaking change is that we no longer try to search for
triple-prefixed lld/mold binaries anymore. However, since there doesn't
seem to be support to build LLVM or mold with triple-prefixed executable
names, it seems better to just not bother with that case.
PR driver/111605
* collect2.cc (main): Do not prepend target triple to
-fuse-ld=lld,mold.