[PATCH] uml: S390 preparation, arch_align_stack

Only x86 and x86_64 use arch_align_stack(), all other subarches have:

 #define arch_align_stack(x) (x)

So, if this definition is found, UML's own arch_align_stack() should be
skipped.

Signed-off-by: Bodo Stroesser <bstroesser@fujitsu-siemens.com>
Cc: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>