[core] Use automatic build tree detection for all resource directories

[guitargeek]

This follows up on a5b1ed9, using the mechanism to automatically detect if we are in the build tree or install tree also for the other resource directories (so far it was only implemented for the include directory as a first test).

Several fallbacks and hacks can be removed because of this change, like the ROOTIGNOREPREFIX variable that was needed to run ROOT in the build tree for the tests.

This change also makes ROOT completely independent of the ROOTSYS environment variable and therefore unblocks #20006.

If one wants to check that all the resource directories (inlcuding RootSys()) are correct, one can use this check:

void checkdirs() {

    std::cout << "Bin       : " << gROOT->GetBinDir() << std::endl;
    std::cout << "Data      : " << gROOT->GetDataDir() << std::endl;
    std::cout << "Doc       : " << gROOT->GetDocDir() << std::endl;
    std::cout << "Etc       : " << gROOT->GetEtcDir() << std::endl;
    std::cout << "Icon      : " << gROOT->GetIconPath() << std::endl;
    std::cout << "Include   : " << gROOT->GetIncludeDir() << std::endl;
    std::cout << "Lib       : " << gROOT->GetLibDir() << std::endl;
    std::cout << "Macro     : " << gROOT->GetMacroDir() << std::endl;
    std::cout << "RootSys   : " << gROOT->GetRootSys() << std::endl;
    std::cout << "SharedLib : " << gROOT->GetSharedLibDir() << std::endl;
    std::cout << "TTFFont   : " << gROOT->GetTTFFontDir() << std::endl;
    std::cout << "Tutorial  : " << gROOT->GetTutorialDir() << std::endl;
}

[github-actions]

Test Results

    22 files      22 suites   3d 11h 10m 7s ⏱️
 3 849 tests  3 848 ✅  1 💤 0 ❌
76 007 runs  75 989 ✅ 18 💤 0 ❌

Results for commit 6c6dee9.

♻️ This comment has been updated with latest results.

[vepadulano]

https://github.com/root-project/root/actions/runs/21481040637/job/61888781030?pr=21018#step:7:18 This error probably means that ROOT cannot even start and the process segfaults.

[guitargeek]

https://github.com/root-project/root/actions/runs/21481040637/job/61888781030?pr=21018#step:7:18 This error probably means that ROOT cannot even start and the process segfaults.

This is fixed by that PR:

• [build] Use CMAKE_INSTALL_<dir> variables consistently in setup.py #21075