Skip missing symbol version section check for executable

Skip missing symbol version section check for executable

Missing symbol version section is a run-time problem only if it will
be referenced dynamically at run-time.  We should skip the check for
locally defined symbol, which isn't referenced by shared library, when
linking executable.

bfd/

	PR ld/18718
	* elflink.c (elf_link_output_extsym): Check symbol version
	section check only if not linking executable, the symbol is
	referenced by shared library or not locally defined.

ld/testsuite/

	PR ld/18718
	* ld-elf/pr18718.c: New file.
	* ld-elf/shared.exp: Run tests for PR ld/18718.