I actually just finished a successful compile. Seems this is unnecessary to document now, but for posterity, here's what I did:
I added
#include <errno.h>
to the following files:
mcw_glob.c
rickr/l_mcw_gob.c
Which fixed the errno problem (my original problem was, as you suggested, caused by a damaged Makefile.INCUDE)
I was getting a "can't stat source" error for cjpeg and djpeg (~ line 1530 of the INCLUDE file), so I took them out of the EXTRAS definition and compiled them separately.
Thanks.