ELF: Properly handle section symbols

ELF: Properly handle section symbols

When defining the section symbol, __start_FOO, for the section FOO:

1. Treat the common symbol, __start_FOO, in input object file as
definition.
2. Clear verinfo.verdef.

bfd/

	PR ld/26094
	* elflink.c (bfd_elf_define_start_stop): Handle common symbols.
	Clear verinfo.verdef.

ld/

	PR ld/26094
	* testsuite/ld-elf/pr26094-1.ver: New fike.
	* testsuite/ld-elf/pr26094-1a.c: Likewise.
	* testsuite/ld-elf/pr26094-1a.rd: Likewise.
	* testsuite/ld-elf/pr26094-1b.c: Likewise.
	* testsuite/ld-elf/pr26094-1b.rd: Likewise.
	* testsuite/ld-elf/pr26094-1c.c: Likewise.
	* testsuite/ld-elf/shared.exp: Run ld/26094 tests.