Add a compat/strtoumax.c for Solaris 8.

Add a compat/strtoumax.c for Solaris 8.

Solaris 8 was pre-c99, and they weren't willing to commit to
the strtoumax definition according to /usr/include/inttypes.h.

This adds NO_STRTOUMAX and NO_STRTOULL for ancient systems.
If NO_STRTOUMAX is defined, the routine in compat/strtoumax.c
will be used instead.  That routine passes its arguments to
strtoull unless NO_STRTOULL is defined.  If NO_STRTOULL, then
the routine uses strtoul (unsigned long).

Signed-off-by: Jason Riedy <ejr@cs.berkeley.edu>
Acked-by: Shawn O Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <junkio@cox.net>