Fix illegal memory accesses in the assembler when attempting to parse corrup tinput...

Fix illegal memory accesses in the assembler when attempting to parse corrup tinput files.

	PR 23054
	* cond.c (s_ifsef): Replace use of obstack_copy with obstack_alloc
	followed by memcpy.
	(s_if, s_ifb, s_ifc, s_ifeqs): Likewise.
	* obj-elf.c (elf_adjust_symtab): Check for local symbols before
	attempting to dereference the sy_next field of a symbol.
	* stabs.c (get_stab_string_offset): Fail if there is no string
	following the stab directive.