elf: Check DT_SYMTAB only on non-IR object

Check DT_SYMTAB only on non-IR object of archive member to avoid crash
on LLVM IR object with NULL elf_tdata.

	PR ld/30811
	* elflink.c (elf_link_is_defined_archive_symbol): Check
	DT_SYMTAB only on non-IR object.