[coverage] Investigate invalid profile data

While working on #18745, I found the root cause for the malformed profile data after migrating to LLVM 16.0.2: it was a call to `__llvm_profile_register_function()` with a bad pointer. Interestingly this pointer contains the address of the `__llvm_profile_runtime` variable that we define to be able to measure coverage on target. It's not clear if this is a compiler bug or if we need to react to another change that occurred some time between LLVM 13 and 16.