[Driver] Gnu.cpp: remove unneeded -L lib/gcc/$triple/$version/../../../$triple

After path resolution, it duplicates a subsequent -L entry. The entry below
(lib/gcc/$triple/$version/../../../../$OSLibDir) usually does not exist (e.g.
Arch Linux; Debian cross gcc). When it exists, it typically just has ld.so (e.g.
Debian native gcc) which cannot cause collision. Removing the -L (similar to
reordering it) is therefore justified.