Make the generated .cmake files reproducible.

[lamby]

Whilst working on the Reproducible Builds effort, I noticed that meson did not generate reproducible .cmake files: they include the full path name. This commit not only makes the build reproducible, but it also matches CMake's own behaviour. Specifically, CMakePackageConfigHelpers.cmake does the equivalent transformation using get_filename_component(inputFileName "${_inputFile}" NAME).

I originally filed this in Debian as bug #1000327.

[eli-schwartz]

Huh, that makes a lot of sense... I wonder why this used the whole path in the first place, the cmake module does try to explicitly copy cmake's output.

[lamby]

Perhaps it doesn't usually matter in that infile is usually relative? Either way, its pretty harmless as it's commented anyway. :)

[codecov]

Codecov Report

Merging #9602 (940c13c) into master (809792c) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #9602      +/-   ##
==========================================
- Coverage   67.41%   67.41%   -0.01%     
==========================================
  Files         402      402              
  Lines       85478    85478              
  Branches    17620    17620              
==========================================
- Hits        57626    57625       -1     
- Misses      23245    23246       +1     
  Partials     4607     4607              

Impacted Files	Coverage Δ
mesonbuild/modules/cmake.py	71.96% <100.00%> (ø)
mesonbuild/scripts/vcstagger.py	87.50% <0.00%> (-4.17%)	⬇️

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[eli-schwartz]

We literally mention Any changes to this file will be overwritten by the next CMake run which is untrue as it will be overwritten by the next meson run... that is an irrelevant comment too. :D

Over in my neck of the woods this sort of variation isn't actually tested as build paths are predictable. :/ Thanks for the catch.