PR ld/20828: Move symbol version processing ahead of GC symbol sweep

PR ld/20828: Move symbol version processing ahead of GC symbol sweep

Complement commit b531344c34b0 ("PR ld/20828: Reorder the symbol sweep
stage of section GC") and commit 81ff47b3a546 ("PR ld/20828: Fix linker
script symbols wrongly forced local with section GC") and move symbol
version processing ahead of the symbol sweep stage of section GC, all in
`bfd_elf_size_dynamic_sections', so that version symbols created stay in
the global scope and are not output as local symbols to the dynamic
symbol table in the presence of corresponding symbol definitions pulled
from a DSO involved in a link.

Consolidate the whole of symbol version processing into a single block
from all parts scattered across the function and rearranging the local
variables used as necessary, however leaving the setting of dynamic
entries associated with the DT_VERDEF, DT_VERDEFNUM, DT_VERNEED and
DT_VERNEEDNUM tags and the SEC_EXCLUDE flag for unused `.gnu.version'
section in the original places.

With the rearrangement of code blocks `Elf_Internal_Verneed *t' would
shadow the previous definition of `struct bfd_elf_version_tree *t', so
rename the former variable to `vn'.

	bfd/
	PR ld/20828
	* elflink.c (bfd_elf_size_dynamic_sections): Move symbol version
	processing ahead of the call to `elf_gc_sweep_symbol'.

	ld/
	PR ld/20828
	* testsuite/ld-elf/pr20828-d.sd: New test.
	* testsuite/ld-elf/pr20828-e.sd: New test.
	* testsuite/ld-elf/pr20828-v.od: New test.
	* testsuite/ld-elf/pr20828-v.ver: New test version script.
	* testsuite/ld-elf/pr20828-v.ld: New test linker script.
	* testsuite/ld-elf/pr20828.ld: Add `.gnu.version' and
	`.gnu.version_d'.
	* testsuite/ld-elf/shared.exp: Run the new tests.