arm maketools needs include/asm-arm in place in the build tree.
On normal builds it's always there, of course, but on O= it's created
(by generic code) too late - when we get to asm-offset.h.

	We used to get away with that by accident - creation of
include/asm-arm/arch symlink creates include/asm-arm and it happened
to go before maketools.  However, we did not have such dependency,
so that luck didn't last - now maketools is picked first and we are screwed.

	Both the symlink and maketools are prerequisites of the same
target (archprepare).  This fix is obvious - make the latter explicitly
depend on the former and be done with that.

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