[ELF] Update for LLVM api change

The `Elf_Rel_Impl::setSymbolAndType` method now has the third argument
`IsMips64EL` (like complement methods `getSymbol` and `getType`). While
we do not support linking of MIPS64 ELF object file just pass `false`
to the `setSymbolAndType`.

llvm-svn: 227045