Make this port build properly.

Summary:
It looks like we forgot to add '${SETENV} ${MAKE_ENV}' to the build
script. Right now it ignores the compiler entirely.

Furthermore, regardless of whether a C11 compiler is being used, the
build will fail, for the reason that some C11 headers such as
<stdnoreturn.h> are being used in the code. Instead of trying to fix
that, simply disable this port on FreeBSD <10.1. I have no intent on
ever getting CloudABI to work on FreeBSD 9.

Reviewers: bapt

Reviewed By: bapt

Differential Revision: https://reviews.freebsd.org/D3077