elf: Resolve more relocations into GOT entries

[Arusekk]

So far only relocations pointing to external symbols were considered when filling GOT. Relocations in libc are a different thing, often found in CTF challenges (libc with partial RELRO has many interesting overridable function pointers, like strlen & strchrnul).

[peace-maker]

Nice, is it possible to add a test for this?