PR22150, ld keeps a version reference for gc'd symbols

PR22150, ld keeps a version reference for gc'd symbols

elf_gc_sweep_symbol should run after verdefs are calculated, since
the verdef code creates symbols for the versions.  However,
elf_gc_sweep_symbol needs to run before verrefs so as to not emit
useless verrefs for symbols that are gc'd.

I've also removed a _bfd_elf_link_renumber_dynsyms calls added by
Maciej after I fussed about it when reviewing.  On further examination
the call appears to be unnecessary.  Looking at renumber_dynsyms also
made me realize that the test to exclude .gnu.version has been wrong
since 2016-04-26 (git commit d5486c4372), so fix that too.

	PR 22150
	* elflink.c (bfd_elf_size_dynamic_sections): Garbage collect
	symbols before calculating verrefs.  Don't renumber dynsyms
	after gc.  Exclude .gnu.version when zero or one dynsym.
	Localize some vars and reindent.