Fix grub2 for gcc 4.7.

"-melf_x86_64" is a linker option, prefix it with "-Wl".

Gcc prior to 4.7 seems to pass this option to ld, but 4.7 doesn't.

TEST=Built using gcc 4.7
BUG=None

Change-Id: I5908d34fd0f9dc939581a2eaed5cd20d282c6d3a
Reviewed-on: https://gerrit.chromium.org/gerrit/30486
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Commit-Ready: Han Shen <shenhan@chromium.org>
Tested-by: Han Shen <shenhan@chromium.org>
2 files changed