CMake: also find jconfig.h from libturbojpeg from arch-specific include directory

[illwieckz]

Description

This header file is architecture-dependent and can be stored as:

• /usr/include/i386-linux-gnu/jconfig.h
• /usr/include/x86_64-linux-gnu/jconfig.h

Instead of:

• /usr/include/jconfig.h

That fixes build errors like this:

CMake Error at src/cmake/modules/FindJPEGTurbo.cmake:32 (file):
  file STRINGS file "/usr/include/jconfig.h" cannot be read.
Call Stack (most recent call first):
  src/cmake/checked_find_package.cmake:127 (find_package)
  src/cmake/externalpackages.cmake:139 (checked_find_package)
  CMakeLists.txt:155 (include)

Checklist:

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  This change is too small and not original enough to be subject to copyright.
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  Not applicable.
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  (adding new test cases if necessary).
  Not applicable.
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[lgritz]

I'm not so sure about the FATAL_ERROR here -- if this header can't be found, I think we want only the find_package(JPEGTurbo) to not succeed, and then to fall back on regular find_package(JPEG). We don't want the entire cmake build to fail.

[lgritz]

@illwieckz Any comment or further action on this? In general, I think it's fine except for the FATAL_ERROR part.

[illwieckz]

Sorry, I was busy and totally forgot about it. I'll look at it again.

[lgritz]

@illwieckz Ping -- can you please take a look here at my previous comment and offer an opinion?

[illwieckz]

Changed to a WARNING.

[lgritz]

This line file(STRINGS ...) needs to be inside an if (jconfig_header_file) conditional. If the header is not found, trying to extract strings from it results in a build-breaking cmake error, as you can see from the windows CI job.

[domin144]

Starting with version 2.1.0 libjpeg-turbo provides it's own cmake config files, but they are named different to what is used in oiio cmake files.
I think the line:

checked_find_package (JPEGTurbo

Should be changed to:

checked_find_package (libjpeg-turbo

so that distro provided library is detected if present.

[lgritz]

That's interesting, @domin144. I'm tempted to advise abandoning this PR entirely and instead simply removing FindJPEGTurbo.cmake entirely, relying on jpeg-turbo's exported config, and calling it a day. That will mean that we are raising the floor of JPEG-turbo that we support to 2.1. But since that's still 2.5 years old and this is not a required dependency (we can automatically fall back to libjpeg), I think that would be acceptable.

Opinions?

[lgritz]

I tried the other strategy here: #3987

What do people think of that proposal, which would obviate the need for this one here?