[PATCH] Fix 'make headers_check' on biarch architectures

We generate an <asm/foo.h> which includes either <asm-$ARCH/foo.h> or
<asm-$ALTARCH/foo.h> as appropriate.  But we were doing this dependent on
whether the file in question existed in the _unexported_ tree, not the
exported tree.  So if a file was exported to userspace in one asm- directory
but not the other, the generated file in asm/ was incorrect.

This only changed the failure mode if it _was_ included from a nice #error to
a less explicable #include failure -- but it also gave false errors in 'make
headers_check' output.  Fix it by looking in the right place instead.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>