Introduce a RUNPATH for compiled macros.

[hageboeck]

This follows up on 3161321, where LD_LIBRARY_PATH was removed from roottest.

It cannot be removed without replacement for tests that compile macros. Either LD_LIBRARY_PATH or RUNPATH is needed for those: When ROOT is installed in the system, or when an LD_LIBRARY_PATH is set such that a different ROOT installation is visible, compiled macros can fail. The sequence of events is as follows:

• roottest compiles a macro into an .so
• In a subsequent test, that .so is loaded.
• The dynamic loader will try to load the dependencies of that .so, e.g. libROOTVecOps.so, libCore.so, ... Given that the library being opened (the .so resulting from the macro) doesn't have any RUNPATHs set, the ROOT libraries it depends on are searched for first in LD_LIBRARY_PATH and then in the system.
• If a library of another ROOT is found in one of those two locations, the whole chain of library loads starts, opening all ROOT libraries that the last library found depends on, loading e.g. /usr/lib64/libCore.so and similar. This will provoke a lot of warnings, because TClassTable is already populated, and potentially crashes the program.

Therefore, in this PR, a RUNPATH is added for ACLiC libraries on Linux and Mac. TSystem::GetMakeSharedLib() by default now contains $RPath, which gets expanded to -Wl,-rpath,<ROOT library path>.

[guitargeek]

LGTM! It would just be nice to add some comment avoid the a possible more future-proof solution as a TODO, so we maybe attract effort to implement RUNPATH embedding in ACLiC.

[github-actions]

Test Results

    23 files      23 suites   4d 4h 20m 10s ⏱️
 3 816 tests  3 816 ✅ 0 💤 0 ❌
80 418 runs  80 418 ✅ 0 💤 0 ❌

Results for commit 7f5bc86.

♻️ This comment has been updated with latest results.

[hageboeck]

LGTM! It would just be nice to add some comment avoid the a possible more future-proof solution as a TODO, so we maybe attract effort to implement RUNPATH embedding in ACLiC.

In fact, that what I did now. 🙂

[guitargeek]

Thank you very much, awesome!

It's definitely also a step in the right direction because it unifies macOS and Linux behavior, and synchronizes root-config --libs and gSystem->GetMakeSharedLib().

[vepadulano]

LGTM, remember to squash the second commit before merging.