[MC][ELF] Don't create relocations with section symbols for STB_LOCAL ifunc

We should keep the symbol type (STT_GNU_IFUNC) for a local ifunc because
it may result in an IRELATIVE reloc that the dynamic loader will use to
resolve the address at startup time.

There is another problem that is not fixed by this patch: a PC relative
relocation should also create a relocation with the ifunc symbol.

llvm-svn: 362767