[PATCH] alpha xchg fix

alpha xchg has to be a macro - alpha disables always_inline and if that
puppy does not get inlined, we immediately blow up on undefined reference.
Happens even on gcc3; with gcc4 that happens a _lot_.

Signed-off-by: Al Viro <viro@parcelfarce.linux.theplanet.co.uk>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>