Use version index 1 for defined symbols

It's reasonable to use version index 0 for undefined
symbols, so let's continue doing that.  For defined (global)
symbols that aren't otherwise versioned continue using
VER_NDX_GLOBAL (partly reverting behaviour introduced in
commit f685e395).

bfd/
	PR ld/33577
	* elflink.c (elf_link_output_extsym): Don't set noversion
	for defined syms.

ld/
	PR ld/33577
	* ld-elfvers/vers16.dsym: Add back the "Base" version for
	defined syms.