This may be in purpose in which case please close.
I note that in makefile.vc6 (and derivatives) the debug objects usually have 'd' appended to their names (nonblockd.obj rawstrd.obj &c), but slist_wc.obj doesn't. The net result is that if you type
nmake .... release
name .... debug
NMAKE : warning U4004: too many rules for target 'slist_wc.obj'
makefile.vc6: use d suffix on debug object
To allow both release and debug builds in parallel.
Reported-by: Rod Widdowson