elf: Fix elf/tst-pldd with --enable-hardcoded-path-in-tests (BZ#24506)

elf: Fix elf/tst-pldd with --enable-hardcoded-path-in-tests (BZ#24506)

The elf/tst-pldd (added by 1a4c27355e146 to fix BZ#18035) test does
not expect the hardcoded paths that are output by pldd when the test
is built with --enable-hardcoded-path-in-tests.  Instead of showing
the ABI installed library names for loader and libc (such as
ld-linux-x86-64.so.2 and libc.so.6 for x86_64), pldd shows the default
built ld.so and libc.so.

It makes the tests fail with an invalid expected loader/libc name.

This patch fixes the elf-pldd test by adding the canonical ld.so and
libc.so names in the expected list of possible outputs when parsing
the result output from pldd.  The test now handles both default
build and --enable-hardcoded-path-in-tests option.

Checked on x86_64-linux-gnu (built with and without
--enable-hardcoded-path-in-tests) and i686-linux-gnu.

	* elf/tst-pldd.c (in_str_list): New function.
	(do_test): Add default names for ld and libc as one option.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>