Taking another look at the patch, I'm not real keen on the C/LDFLAGS section. I think if we want to support setting these, we should fully override the default settings (otherwise you can't specify certain options that are in the defaults), and avoid splitting them (which probably means changing the spawn() call to not quote arguments - right now the .split() logic is just wrong).

I'm sorry this is tough to get together - the distutils compilers are really fragile, which is why we would really rather migrate people off them onto some other build framework. Right now though, that framework doesn't exist. (One potential starting point is my msbuildcompiler at https://github.com/zooba/pyfindvs/tree/master/pyfindvs/msbuildcompiler will generate a .vcxproj file and build it, which allows much more reliable behaviour for options and detecting installs.)