elf: Verify base symbol version works properly

Add a testcase to verify that VER_NDX_GLOBAL can be used with

asm (".symver foo_base, foo@");

to create the base version to provide an unversioned compatible symbol.

	PR ld/33577
	* testsuite/ld-elfvers/pass.out: New file.
	* testsuite/ld-elfvers/pr33577-unversioned.c: Likewise.
	* testsuite/ld-elfvers/pr33577-unversioned.rd: Likewise.
	* testsuite/ld-elfvers/pr33577-versioned.c: Likewise.
	* testsuite/ld-elfvers/pr33577-versioned.rd: Likewise.
	* testsuite/ld-elfvers/pr33577.map: Likewise.
	* testsuite/ld-elfvers/pr33577a.c: Likewise.
	* testsuite/ld-elfvers/pr33577b.c: Likewise.
	* testsuite/ld-elfvers/vers.exp: Run ld/33577 tests.

Signed-off-by: H.J. Lu <hjl.tools@gmail.com>