[MIPS] Workaround for bug in gcc -EB / -EL options.

Certain gcc versions upto gcc 4.1.1 (probably 4.2-subversion as of
2006-10-10 don't properly change the the predefined symbols if -EB / -EL
are used, so we kludge that here.  A bug has been filed at
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29413.

Signed-off-by: Ralf Baechle <ralf@linux-mips.org>