[tlbuild] PPC builds

[Johannes Hielscher]

Am Sun, 8 Mar 2020 16:07:29 -0600
schrieb Karl Berry <karl at freefriends.org>:

>     jh> You run ./Build --enable-arm-neon=check?  
> 
>     mm> Is there any chance to somehow make this work out of the box
>     mm> without  
>     extra flags?
> 
> Can anyone dream up a simple program that can be compiled to determine
> if it is needed? (Not that I'm going to be looking at this any time
> soon.) -k
> 

I'm not sure if we need a test conditional for this at all.

Platforms that don't have NEON (anything non-ARM) don't care about this
option. Sounds like just adopting =check as an implicit default for
libpng configure.

AFAICS, there is only one practical case where configuration of libpng's
NEON code paths matter at all, i. e. build host capabilities (checked at
compile time by this flag) and target differ: if you want to compile
with compatibility for low-end/ancient 32-bit ARM boards (1st gen RPi,
Simon?) on more modern hardware. And manually adding
--enable-arm-neon=no just for these cases seems a reasonable compromise
at a semantically sensible place.

Best,
Johannes