The two functions have identical semantics, including safely returning
NULL when NULL is passed in (which POSIX strdup does not guarantee).

Some callers could probably be adjusted to call libc strdup directly,
when we know the input is non-NULL.
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Daniel Stone <daniel@fooishbar.org>
Backported-to-NX-by: Ulrich Sibiller <uli42@gmx.de>