[PATCH] ppc32: add <linux/compiler.h> to <asm/sigcontext.h>

On ppc32, <asm/sigcontext.h> uses __user, but doesn't directly include
<linux/compiler.h>.  This adds that in.  Without this, glibc will not
compile.

Signed-off-by: Tom Rini <trini@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>