Further build system tweaks for MinGW/Win32 builds
no longer hard-code the mingw path
set the CFLAGS up on Win32 builds to find the local
include directory, which is needed for regex.h
if configure sets CPP_SIMPLE to "gcc -E", then we need
to split this into CPP_SIMPLE/CPP_SIMPLE_ARGS, otherwise
the checks in libpcp pmns.c are completely busted and can
even be made to find the wrong binary (very obscure case).
Further build system tweaks for MinGW/Win32 builds