Export <linux/a.out.h> to userspace again.

This seems to have been removed accidentally in commit
ed7b1889 ("Unexport asm/page.h"), but
wasn't supposed to have been -- the original patch at
http://lkml.org/lkml/2007/10/30/144 just moved it from $(header-y) to
$(unifdef-y)
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Acked-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/Kbuild

@@ -166,6 +166,9 @@ unifdef-y += acct.h
 unifdef-y += adb.h
 unifdef-y += adfs_fs.h
 unifdef-y += agpgart.h
+ifeq ($(wildcard include/asm-$(SRCARCH)/a.out.h),include/asm-$(SRCARCH)/a.out.h)
+unifdef-y += a.out.h
+endif
 unifdef-y += apm_bios.h
 unifdef-y += atalk.h
 unifdef-y += atmdev.h