[m-rev.] for review: fix asm_fast grades with GCC 6

[Zoltan Somogyi]

On Wed, 6 Jul 2016 10:48:36 +1000 (AEST), Julien Fischer <jfischer at opturion.com> wrote:
> They just bumped their major version number

I think this is likely to happen again with gcc 7, gcc 8 etc.

We can either add them to the case patterns as well right now,
or change the configure script to simply test for the presence
of the -fno-tree-dominator-opts option, and use it if it exists.
If the tree dominator optimization ever starts working properly
for us, we can worry about it then.

Zoltan.