add MSVC support to win32/GNUmakefile

add MSVC support to win32/GNUmakefile

-copy things from makefile.mk to GNUmakefile
-rework CFG_VARS to escape "s. Previously on gmake GCC builds, all "s
 inside the CFG_VARS vars were dropped from Config_heavy.pl due to
 command line parsing (dmake uses --cfgsh-option-file and a temp file,
 nmake escapes). Due to gmake's very poor temp file handling, keep it as
 a cmd line and dont convert it to a temp file. What vars to escape was
 modeled on the nmake makefile.