--with-devkit doesn't control nmake

Windows devkits contain an nmake.exe, but the configure and make scripts do not define and consistently use an NMAKE variable to make sure the devkit version is used, as many other commands do.

I had assumed that my builds were using the nmake.exe from the same devkit toolchain as the compilers, etc., but in fact I was using nmake from VS2005, as provided by my company's devops department on my entitlement machine.