Description of problem:

SCSI driver modules have this unfortunate habit that they do
'#include "scsi_module.c"'.  For example, in 
/usr/src/linux-2.6.9-1.6_FC2/drivers/scsi there is 58 .c file
with that line.  So one could reasonably expect that various
"external" drivers for such devices will repeat that pattern.

Here is the catch; if you will do for such driver something
like:

make CFLAGS=... -C /lib/modules/$(uname -r)/build M=$(PWD) modules

with CFLAGS set as required, then on FC3 this fails because
"scsi_module.c" (really an include file) is nowhere to be found
while it truly should sit under ../build/driver/scsi/.

A driver _could_ supply its own copy of scsi_module.c but there
is no guarantee that this will not get later out of sync and,
besides, it is not likely to be there as so far such extra copy
was not ever needed.  Just to be sure we are talking here about
a GPL code.

I have no idea of other subsystems are doing a similar trickery.
Got hit on SCSI. :-)