configure: fix cflags not getting set in all variants
revert 'silence warning' part of cd27a0c3f9b20423c28c03e7501988773464a950
ia32: explicitely specify immediate type in imm matchers

Some instructions liks shifts or out/in can only handle some forms of
immediates. Make matchers respect that.

This fixes backend/ia32_shl.c, although the real question here is
probably why that program wasn't folded to a point where the middleend
would reduce the shift amount anyway because of the modulo shift mode.
Do not create ssize_t typedef on MinGW.
Avoid the word environ since it is a macro on MinGW.
Make test python3-compatible.
Remove dependency on the six python library

We already ship with a jinja2 equivalent anyways
Always use a list for python3 compatibility.
Undef __USE_BSD if it was not defined before.