travis: Move glibc backwards in time

travis: Move glibc backwards in time

This commit updates the compilers for many of the artifacts that we're producing
on Travis. These compilers are all compiled by crosstool-ng as they're currently
done for the images in which we're building all our cross compiled compilers.

The purpose of this commit is that when we ship binaries the artifacts won't
require a newer glibc, but rather be as compatible as possible with Linux
distributions by working with a very old version of glibc.

This commit always allocates a new matrix entry for the i686/x86_64 builder.
This builder is dedicated to just producing artifacts and eventually we'll
expand it to building other tools like Cargo and the RLS. The other builders
testing i686 and x86_64 won't use these historical toolchains.