Fix multiple problems with DLL generation.

ld	* pe-dll.c (make_head): Prefix the symbol name with the dll name.
	(make_tail, make_one, make_singleton_name_thunk): Likewise.
	(make_import_fixup_entry, make_runtime_pseudo_reloc): Likewise.
	(pe_create_runtime_relocator_reference): Likewise.
	(pe_dll_generate_implib): Set dll_symname_len.
	(pe_process_import_defs): Likewise.

binutils
	* dlltool.c (main): If a prefix has not been provided, attempt to
	use a deterministic one based upon the dll name.