[v3] set timeout higher

[Benjamin Kosnik]

> Doesn't this override any timeout I might have specified? On my box, I need
> a lot more than 600 s. For example:

Yes, it looks like it does. Sorry.

For instance, this no longer works correctly:
time make check RUNTESTFLAGS="-v -v -v -v --tool_opts timeout=300"

Now that I look around for this, I see another complaint, from Christian Joensson.

I've created a bugzilla entry to describe this issue here:
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28870

best,
benjamin