libffi in GCC 4.2 needs cachectl.h to do its cache flushing.  But we
don't currently export it.  I believe this patch should do the trick.
Signed-off-by: NMatthew Wilcox <matthew@wil.cx>
Signed-off-by: NGeert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>