ld: sprintf sanitizer null destination pointer

	* configure.ac (stpcpy): AC_CHECK_DECLS.
	* sysdep.h (stpcpy): Add fallback declaraion.
	* config.in: Regenerate.
	* configure: Regenerate.
	* emultempl/pe.em (open_dynamic_archive): Use
	stpcpy rather than sprintf plus strlen.
	* emultempl/pep.em (open_dynamic_archive): Likewise.
	* emultempl/xtensaelf.em (elf_xtensa_before_allocation): Use
	auto rather than malloc'd buffer.  Use sprintf count.
	* ldelf.c (ldelf_search_needed): Use memcpy in place of sprintf.
	* pe-dll.c (pe_process_import_defs): Use string already formed
	for alias match rather than recreating.