Allow TLS access to work in gdb.server/no-thread-db.exp

Allow TLS access to work in gdb.server/no-thread-db.exp

The patches later in the series add GDB-internal TLS support for
certain targets.  This commit updates the "print foo" test in
gdb.server/no-thread-db.exp to accept either a TLS failure (when
libthread_db isn't available) or printing the correct answer, which
will occur when GDB's internal TLS address resolution can be used.

I'm making this change prior to the commits which actually add
the GDB-internal TLS support in order to avoid tripping regression
testers.

Tested-By: Luis Machado <luis.machado@arm.com>
Approved-By: Luis Machado <luis.machado@arm.com>