[CI] Update to Ubuntu 18.04 Docker images

[Frenzie]

See koreader/virdevenv#57 and koreader/virdevenv#62

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This change is 

[Frenzie]

@pazos Actually, do you know which CMake F-Droid uses? I just realized the second commit may be a bit overenthusiastic.

[pazos]

@Frenzie: https://packages.debian.org/stretch/cmake (3.7.2)

There's also a backport: https://packages.debian.org/stretch-backports/devel/cmake (3.16.3) that should be available to install via sudo apt-get in https://gitlab.com/fdroid/fdroiddata/-/blob/master/metadata/org.koreader.launcher.yml#L21

[Frenzie]

Thanks. Well, I'll just revert that second commit. I don't think CMake <3.11 really gives us much extra anyway, although I do vaguely seem to recall @NiLuJe complaining about CMake <3.7 recently?

[NiLuJe]

Whatever passes as "modern" CMake would be great^Wless terrible ;).

[Frenzie]

CMake 3+ and especially 3.4+ is called "modern" CMake afaik. :-P

[NiLuJe]

As a point of reference, I can't even install anything older than 3.13 over here ;p.

[Frenzie]

@NiLuJe Sidenote, are you familiar with this argument fs by any chance? That's for the Sony build.

  CXXLD    libdjvulibre.la
libtool:   error: cannot find the library '' or unhandled argument 'fs'
Makefile:527: recipe for target 'libdjvulibre.la' failed
make[3]: *** [libdjvulibre.la] Error 1
make[3]: Leaving directory '/home/ko/base/thirdparty/djvulibre/build/arm-linux-gnueabihf/djvulibre-prefix/src/djvulibre/libdjvu'
Makefile:429: recipe for target 'all-recursive' failed
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory '/home/ko/base/thirdparty/djvulibre/build/arm-linux-gnueabihf/djvulibre-prefix/src/djvulibre'
Makefile:361: recipe for target 'all' failed
make[1]: *** [all] Error 2
make[1]: Leaving directory '/home/ko/base/thirdparty/djvulibre/build/arm-linux-gnueabihf/djvulibre-prefix/src/djvulibre'
ninja: build stopped: subcommand failed.
Makefile.third:163: recipe for target 'build/arm-linux-gnueabihf/libs/libdjvulibre.so.21' failed
make: *** [build/arm-linux-gnueabihf/libs/libdjvulibre.so.21] Error 1

Exited with code exit status 2

[NiLuJe]

@Frenzie: That doesn't ring a bell, no. Hard to say what's happening without a verbose build to see the crazy libtool command line ;).

[Frenzie]

The Android image issue should be resolved in koreader/virdevenv#65.

I hadn't realized it was pulling in openjdk-11 (and was therefore defaulting to it).

tl;dr Should be almost done.

[jimman2003]

Well missed the chance to request cmake 3.11..next time..

[Frenzie]

Just state your reasons.

[jimman2003]

Well FetchContent and optimisations :)

[Frenzie]

Could you please be a lot more concrete?

[jimman2003]

Cmake 3.13 has Quality of life changes...https://cmake.org/cmake/help/latest/release/3.13.html#id8 Maybe better…
Yeah… new dev easilly excitable..

[Frenzie]

But what do you want to do with FetchContent? How is DownloadProject insufficient? Which specific optimizations would be made possible?

[jimman2003]

It ensures no duplicating of dependencies thoughout the project tree..

[Frenzie]

Which duplication are you referring to?

[jimman2003]

Of source files ,no double downloads

[Frenzie]

Which double downloads are you referring to?

[jimman2003]

No specific examples... I guess our big tree can can be help by caching deps that may be used in many subprojects