maintainer-feedback requested: [Bug 293703] multimedia/ffmpeg4: configure error with GLSLANG option set (libglslang not found)

Bugzilla Automation <bugzilla@FreeBSD.org> has asked freebsd-multimedia
(Nobody) <multimedia@FreeBSD.org> for maintainer-feedback:
Bug 293703: multimedia/ffmpeg4: configure error with GLSLANG option set
(libglslang not found)
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=293703



--- Description ---
if one attempts to use GLSLANG (libglslang 16.x) with this port today they get
no further than:

===>  Configuring for ffmpeg4-4.4.4_30
ERROR: libglslang not found

but this was already fixed for multimedia/ffmpeg back when that was only at
6.x...and then either not needed for 8.x or shaped differently enough that i
missed it when i took a quick look

now, i simply deleted "-lSPVRemapper" from the plus side of our
ffmpeg4/files/patch-configure as it currently sits and kept it moving along to
achieve GreatSuccess™. however, the fix developed by Hiroki Tagato in PR#289912
seems to better respect earlier libglslang versions (if any of those are still
around) while my ham fisted approach might not. i dont believe his patch with
the extra logic applies cleanly to ffmpeg4 without adjustment

tbh "success" here just means configured, built and packaged; i havent found an
occasion to subject this to any thorough test suite of runtime behavior.
perhaps someone more familiar with this particular combination of tools can
chime in with a thumbs up before i get around to it