[tlbuild] asy2.43 attempt, please

[Karl Berry]

    now see that he only switches to gc-7.6.0 on the Mac. 

Yes, he said there were problems with 7.6.0 on Windows, so couldn't
downgrade in general :(.

    is important to realize that the Mac doesn't use or have wget.

I'll tell him, but I'm sure he just copied the general message, and
it's not a bad thing for people to learn that curl and wget both
do the same basic thing.

    autoconfig ALWAYS means we should quit because something is wrong

Indeed. I've rerun autoconf in asy now and committed the new
configure. I surmise that John made a one-line change to configure.ac
and forgot to rerun before making the release. Hope it goes better now.
Have a nice day :).  --best, karl.

P.S. This was the change in configure:
-test "$CXXFLAGS" || CXXFLAGS="-std=c++11"
+test "$CXXFLAGS" || CXXFLAGS=""