Install files in deterministic order

[bmwiedemann]

It might not matter much, but it makes for nicer builddir-diffs without variations in install-log.txt

This PR was done while working on reproducible builds for openSUSE.

[eli-schwartz]

The install-log.txt should not normally matter, as it is only used internally by ninja uninstall.

[bmwiedemann]

Nevertheless it adds noise to the builddir-diff when I am debugging other reproducible-builds issues. So I'd appreciate this being merged, if it does not cause problems.

[eli-schwartz]

I'm not certain I understand what the goal is of diffing the builddir instead of the install dir. There are many files in the builddir that can vary, and anything inside of meson-*/ directories can essentially be assumed to be completely unpredictable databases of fuzz.

[bmwiedemann]

It is one of my approaches to debugging unreproducible build results. e.g. if you have variations in a .so file, it often comes from variations in a .o file which might come from variations in a generated .c or .h or other intermediate file (that only exist in the build dir, but not the install dir).

[eli-schwartz]

How do you deal with the test log, which is inherently random and must be in order to run parallel tests? This is just one example of things in the build directory which are private to meson and not build outputs, that may be random -- and it too is a log file.

Log files are inherently unpredictable, so I don't think it makes much sense to try to guarantee it will be reproducible. It should just be excluded from the diff.