Use dladdr to keep libtbbmalloc loaded on POSIX

[emilazy]

Description

This fixes issues that arise when libtbbmalloc cannot be loaded by relative path, makes the behaviour consistent with the Windows code path, and eliminates the duplication of MALLOCLIB_NAME.

Fixes # - issue number(s) if exists

Type of change

Choose one or multiple, leave empty if none of the other choices apply

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• bug fix - change that fixes an issue
• new feature - change that adds functionality
• tests - change in tests
• infrastructure - change in infrastructure and CI
• documentation - documentation update

Tests

• added - required for new features and some bug fixes
• not needed

Probably too difficult to test. I confirmed that this stops the test suite crashing on program exit on macOS in Nixpkgs, though.

Documentation

• updated in # - add PR number
• needs to be updated
• not needed

Breaks backward compatibility

• Yes
• No
• Unknown

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[emilazy]

It seems like RTLD_NODELETE may be a better solution to the general problem here, by the way. But I only went for the most direct local fix for the problem we were seeing.

[emilazy]

Looks like this is (nondeterministically?) causing problems on Linux, and I don’t know why :(

My guesses (e.g. needs RTLD_GLOBAL?) seem like they should apply equally to the previous state of the code.

[emilazy]

I guess this was the same thing as:

oneTBB/src/tbb/dynamic_link.cpp

Lines 382 to 391 in 91af3ae

	// There is an use case, when we want to find TBB library, not just some shared object
	// providing "dynamic_link" symbol (it can be shared object that directly includes
	// dynamic_link.cpp). For this case we use a public TBB symbol. Searching for public symbol
	// in every case leads to finding main executable instead of TBB library on some version of
	// Linux.
	#if DYNAMIC_LINK_FIND_LIB_WITH_TBB_RUNTIME_VERSION
	static void *func_from_lib = (void*)&TBB_runtime_version;
	#else
	static void *func_from_lib = (void*)&dynamic_link;
	#endif

Switching to a private function fixed it. Let me know if you want to add an #if for this one too.