More x2 WIP for GCC 4.8.2 MinGW-w64/MSYS2 path issue

.. it can now build the compiler, but then we fall over installing
kernel headers with the error:

linux-2.6.33.20/scripts/basic/fixdep.c:108:22:
fatal error: sys/mman.h: No such file or directory

Although it seems to build ok, calling configure with relative
paths is a less invasive approach so I will try at some point and
drop the 4.8.2 patch if it works.