[tlbuild] aarch64: libpng, revisited

[Johannes Hielscher]

Hi builders,


History repeats itself. I am tackling the TL build on AArch64, but
stumbled (once again) over libs/libpng. Manual interaction is needed to
get TL downstream (libs/gd is always the first to complain) to cooperate
with the libpng's nouveau hardware extensions (NEON instructions).

./Build --debug --disable-xindy
[…]
checking for png_create_read_struct... no
configure: error: libpng not found
=== configuring in gd failed

This reminded me to similar issues of Mojca's, some two years ago, on
other not-so-mainstream platforms:
https://tug.org/pipermail/tlbuild/2017q2/003820.html
though the details may differ, depending on the platform-dependent code
paths within libpng.

There was quite some ARM work on the libpng upstream side, as mentioned
in the libpng-1.6.36 changelog. Did this trigger build failure?
I remember that for TL2018 (trunk/pretest, and branch2018), Karl's
silver bullet (-r45971) was --enable-arm-neon plus persuading
autotools to include all the platform-related files into the library.

So was it this time (patch in the attachment). Plus reautoconf's bless
for Makefile.in, gd is now happy with that libpng build on AArch64,
so the rest of the build runs fine (xindy and asy not tested yet).


Best,
Johannes
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