[tlbuild] aarch64/armv8h binary distribution?

[Karl Berry]

Hi Johannes,

    -DPNG_ARM_NEON into libpng's CPPFLAGS

env TL_COMPILER_GFLAGS="-DPNG_ARM_NEON -g" ./Build -g

should add the stated -D to all compilers, as well as the usual -g.
(I don't know offhand whether C or C++ or both are involved here.)
I assume it won't hurt to have that -D everywhere.

    [0] https://sourceforge.net/p/libpng/bugs/230/ 

That post is not clear to me, since it's also mentioned to merely change
one case statement in configure.ac instead of doing all the other
stuff. It seems. And whatever was actually committed is not linked, that
I can see. I will look at the final release when I have a chance.

    TL_CONFIGURE_ARGS="--enable-arm-neon=yes"; distributing ...

Wow, impressive efforts :). I can't say why they didn't work, but we
presumably don't want (do we?) to unconditionally define it on all
platforms anyway ... --thanks, karl.