-Bsymbolic-functions is incompatible with ASan

[Max]

The linker flag -Bsymbolic-functions is default on Ubuntu (see `dpkg-buildflags --get LDFLAGS`). It is not default on Debian.

On Debian the `libclang_rt.asan-x86_64.so` exports `__asan_region_is_poisoned` as dynamic relocatable. On Ubuntu it is not relocatable. This is because of the linker flag just mentioend.
The impact is that on Debian, ASan will use the stub `__asan_region_is_poisoned` defined by the main binary.
On Ubuntu, ASan will use the `__asan_region_is_poisoned` from ASan, because it is statically referenced.

This can be checked using the following command:

```console
$ objdump --dynamic-reloc $(clang -print-file-name=libclang_rt.asan-x86_64.so) | grep __asan_region_is_poisoned
# Debian: 00000000001091c0 R_X86_64_JUMP_SLOT __asan_region_is_poisoned@@Base
# Ubuntu: not found
```

This is problematic for the symbol `__asan_default_options`. Users can implement this function to configure ASan. This only works on Debian and not on Ubuntu, because Ubuntu's __asan_default_options is not relocatable. This bug was reported here: https://bugs.launchpad.net/ubuntu/+source/llvm-defaults/+bug/1964487

I'd suggest the following patch to the LLVM/Clang package:

ifneq (,$(LDFLAGS))
  LDFLAGS := $(filter-out %-Bsymbolic-functions,$(LDFLAGS))
endif

Here is the related bug report for the LLVM project: https://github.com/llvm/llvm-project/issues/62431

[Max (maxammann)]

Another solution might be to allow-list certain functions using --dynamic-list