in reply to MakeMaker tailoring

Do you have to make and install the EnvProcessDll dll separately? If not, you might take the approach of Math::FFT; in this, there's an XS file (FFT.xs), plus a couple of pure C files (arrays.c and fft4g.c) to supply some needed functions. The associated Makefile.PL:
my %opts = ( 'NAME' => 'Math::FFT', 'VERSION_FROM' => '', 'OBJECT' => 'FFT.o fft4g.o arrays.o', ); WriteMakefile(%opts);
writes a Makefile to compile and link all the files needed to build the extension.