POSIX reserves the RTLD_ namespace, and this is already reflected in our
conform tests.
Note: RTLD_DEFAULT and RTLD_NEXT appear in IEEE Std 1003.1-2004. Many
systems (e.g. FreeBSD, musl) just define the macros unconditionally.
Reviewed-by: Florian Weimer <fweimer@redhat.com>
Tested-by: Florian Weimer <fweimer@redhat.com>