How do I process the configure file when cross-compiling with mingw?

Question

I have a small open source program that builds with an autoconf configure script.

I ran configure I tried to compile with:

make CC="/opt/local/bin/i386-mingw32-g++"

That didn't work because the configure script found include files that were not available to the mingw system.

So then I tried:

./configure CC="/opt/local/bin/i386-mingw32-g++"

Is that the right way to do it?