Thanks for your reply.
> gnumake man page does show a -C option.
Yes, in
http://www.mcsr.olemiss.edu/cgi-bin/man-cgi?make
I saw from "OPTIONS"
-C dir
Change to directory dir before reading the makefiles or doing
anything else. If multiple -C options are specified, each is
interpreted relative to the previous one: -C / -C etc is equiva-
lent to -C /etc. This is typically used with recursive invoca-
tions of make.
From the description, I think my way to simulate this option (in my question 2) is OK.
> Does the software require you use gnumake?
Not actually. The project I use has a Makefile.common for linux as well as one for SunOS. However the Makefile which is shared by both contains "make -C". Thus I think probably it's because linux has -C support for make, which may come from GNU make.