elf: Support elf/tst-dlopen-aout in more configurations

dlopen can no longer open PIE binaries, so it is not necessary
to link the executable as non-PIE to trigger a dlopen failure.

If we hard-code the path to the real executable, we can run the test
with and without hard-coded paths because the dlopen path will not
be recognized as the main program in both cases.  (With an explict
loader invocation, the loader currently adds argv[0] to l_libname
for the main map and the dlopen call suceeds as a result; it does
not do that in standard mode.)