This was used in the old dark age of 2.4, ARCH_CFLAGS doesn't work any more
since some time, and UM_FASTCALL was never used in 2.6.

Instead, reintroduce the thing more properly now, directly in
include/asm-um/linkage.h.
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>