[PR21703]Adjust pr21703 tests on various targets.

[PR21703]Adjust pr21703 tests on various targets.

xfail tests for certain targets.
Check shared library support for shared test.
Relax pr21703-r.sd and pr21703-shared.sd with additional "#..." pattern lines.

ld/

	* testsuite/ld-elf/elf.exp: xfail pr21703 tests on specific targets.
	Only run shared lib test for targets which support it.
	* testsuite/ld-elf/pr21703-r.sd: Adjust the expected output.
	* testsuite/ld-elf/pr21703-shared.sd: Likewise.