[tlbuild] build info updates

[Johannes Hielscher]

Am Mon, 1 Mar 2021 16:14:49 -0700
schrieb Karl Berry <karl at freefriends.org>:

> So, below is the info I have now in Build/source/README. Johannes,
> Simon, Marc, Ken, please let me know about any updates.

> ------------------------------------------------------------
> aarch64-linux:
>   aarch64 Debian GNU/Linux 10 (buster)
>   gcc (Debian 8.3.0-6) 8.3.0
>   ./Build --enable-arm-neon=check
> 

Nothing new. FYI, the build works identically in an OpenSuSE Leap 15.2
environment.

The --enable-arm-neon stunt is still needed, otherwise configuring gd
to link against libpng will fail, on these systems where assembler
code branches are not automatically enabled by their respective
./configure logic.

Best,
Johannes