try to disable certain gcc 4.8 optimizations that make greenlet crash

we workaround our "incorrect and flimsy hacks" here by trying to
compile with -fno-tree-dominator-opts.

see https://github.com/python-greenlet/greenlet/issues/28 and
https://github.com/python-greenlet/greenlet/pull/29
Merge branch 'wip-issue28-configure-compiler'

that's the branch where we try to disable certain gcc optimizations.