Build in freestanding mode (fixes GCC 4.8 build)
Build in freestanding mode (fixes GCC 4.8 build)

I have no idea why we weren't doing this already.  Pass -ffreestanding
to GCC to make sure we get a freestanding C environment (rather than
the default "hosted" environment).  With this change, GCC 4.8 can now
build sv6 without segfaulting.  There's no obvious change when
building with GCC 4.7, but it probably makes our build process more
robust.

aclements/sv6,bowlofstew/sv6,bowlofstew/sv6,aclements/sv6,bowlofstew/sv6,bowlofstew/sv6,aclements/sv6,bowlofstew/sv6,aclements/sv6,aclements/sv6