Revert "ELF: Add /lib and /usr/lib as default search paths."

It was causing errors like

/lib/libc.so.6 is incompatible with elf_x86_64

when linking on Fedora.

Every system has different default paths. It seems better to just trust
the driver to pass the correct -L options.

This reverts commit 262910.

llvm-svn: 262941