Lower requirements for gcc and clang

[sebastian-wieczorek]

@joka921 Lower the requirements for gcc and clang for cpp17

[joka921]

@sebastian-wieczorek
I have just started the automated checks, but I am somewhat expecting them to fail
(because even GCC 9.4 probably doesn't compile QLever in C++17 mode because of Coroutines and all the other things).

But a good idea would be to make the lowering of the versions dependent (at least for now) on a different parameter,
(independent from USE_CPP_17_BACKPORTS , and then add a separate GitHub Action that doesn't compile all of QLever, but only some explicit targets (those that already work with C++17, either because they are working out of the box, or because they have already been backported.)
But If you want we can discuss this further.

[sparql-conformance]

Conformance check passed ✅

No test result changes.

Details: https://qlever.cs.uni-freiburg.de/sparql-conformance-ui?cur=25e0ec2a15219dbd8d7df1cb7b9c8d5d5bc4f5e9&prev=97c195aaf9e249f43a6417f99ea93f7e94831f39

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.87%. Comparing base (97c195a) to head (25e0ec2).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1693      +/-   ##
==========================================
+ Coverage   89.84%   89.87%   +0.02%     
==========================================
  Files         389      389              
  Lines       37268    37268              
  Branches     4202     4202              
==========================================
+ Hits        33482    33493      +11     
+ Misses       2485     2478       -7     
+ Partials     1301     1297       -4     

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud