Put soname in the version definition section

Put soname in the version definition section

commit 902e9fc76a0ec9f642cefa71ef88cca1c675ad54
Author: Maciej W. Rozycki <macro@imgtec.com>
Date:   Tue Feb 21 01:46:42 2017 +0000

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

breaks version definition with --version-script --soname.  This patch
fixes it by getting soname index before generating the version definition
section.

bfd/

	PR ld/21389
	* elflink.c (bfd_elf_size_dynamic_sections): Get soname index
	before generating the version definition section.

ld/

	PR ld/21389
	* testsuite/ld-elf/pr21389.map: New file.
	* testsuite/ld-elf/pr21389.s: Likewise.
	* testsuite/ld-elf/pr21389a.d: Likewise.
	* testsuite/ld-elf/pr21389b.d: Likewise.
	* testsuite/ld-elf/pr21389c.d: Likewise.