syslimits.h not built for canadian-cross

[Mumit Khan]

When doing a canadian cross, gcc build process does not create a 
gcc/include/syslimits.h and that's obviously a bug. It has to do
with the following: stmp-int-hdrs depends on STMP_FIXINC, which
for native or cross builds expands to stmp-fixinc target, which
creates gcc/include/syslimits.h; for canadian cross, STMP_FIXINC
is empty, and no other target creates gcc/include/syslimits.h.

One possible fix is to split stmp-fixinc into two sections -- one
does the actual fixing, and the other just creates the syslimits.h.
Add the syslimits.h target to the dependency list of stmp-int-hdrs.

Regards,
Mumit