Reimplementation of dlOpen for macOS to avoid SIP problems

Functionality to add/problem to solve

SIP (System Integrity Protection) on macOS clears environment variables, which affect behaviour of dynamic linker (DYLD_LIBRARY_PATH). OpenFOAM keeps backup of this variable in FOAM_LD_LIBRARY_PATH and currently it restores DYLD_LIBRARY_PATH in RunFunctions file. This solution is not quite complete, as it (a) requires sourcing of RunFunctions file, (b) additional errors appear depending on a user workflow (ex. #2793 (closed), #2555 (closed)).

The patch solves the problem by iterating through paths stored in backup variable, while loading dynamic library.

Target audience

OpenFOAM users on macOS with SIP enabled.

Proposal

Try to emulate dlopen behaviour: iterate over paths stored in FOAM_LD_LIBRARY_PATH, for each of the paths construct full path to the library, try to load a library using full path.

What does success look like, and how can we measure that?

1. There is no need to restore DYLD_LIBRARY_PATH in RunFunctions.
2. User with SIP enabled can load additional libraries in case files and solver finds them independently of the way the case is executed (from command line, from a script using runApplication function, from a script using foamJob script, etc.)

Funding

Patch implementing the functionality is attached to the issue.

01-dlopen-SIP-remediation.patch

Note

sprintf and vfork are deprecated on macOS, so I also added changes to remove deprecation warnings during compilation.