Move to c++17.

[mgautierfr]

All our compilers should handle c++17. Let's move on.

Following of openzim/libzim#819
Fix #877

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.04% 🎉

Comparison is base (bde737f) 38.87% compared to head (983105c) 38.92%.

❗ Current head 983105c differs from pull request most recent head c38ab3e. Consider uploading reports for the commit c38ab3e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #996      +/-   ##
==========================================
+ Coverage   38.87%   38.92%   +0.04%     
==========================================
  Files          58       58              
  Lines        4000     4008       +8     
  Branches     2200     2204       +4     
==========================================
+ Hits         1555     1560       +5     
+ Misses       1101     1099       -2     
- Partials     1344     1349       +5     

see 4 files with indirect coverage changes

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[veloman-yunkan]

LBTSG-IEDSAP-TM¹

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¹ Looks better than simply good - I even dare say, almost perfect - to me

[kelson42]

@mgautierfr You mean fixes #877 ?