Fixes to pypy.

- Adds c++ to MODGCC4_LANGS. There are a few .cxx files, so this change
  is safe (and cheap).
- Deletes CFLAGS from the Makefile. It isn't longer necessary with my
  patch.
- Adds SETENV and MAKE_ENV in the correct places.
- If someday is necessary to change the level of optimization to a
  number, --opt=something is less confussing than -Osomething.
- Adds a patch with fixes to $CC and $CFLAGS.