Please support the LLVMFuzzerRunDriver interface to enable fuzzing targets that must provide their own main().

Supporting this should be simple, i.e., by putting something like:

int main() { return LLVMFuzzerRunDriver(); } 

in a separate compilation unit (see e.g., libfuzzer) and allow linking without it. So the fuzz target's main can run first, which can call the engine's "main", i.e., LLVMFuzzerRunDriver().

cc: @domenukk