[tlbuild] mktexfmt enabled

[John Minter]

> It turns out that mktexfmt was disabled by default.  I changed that and
> ran autoreconf to update all the configure scripts.
>
> Now when I do a fresh Build, the resulting engines do dynamically make
> their format files.  Hope it works for others too.

Thanks, Karl. All works for me as advertised. I'll test the lowest
common denominator x86_64 binaries when you post them.