[gdb/testsuite] Update gdb startup text in selftest.exp

[gdb/testsuite] Update gdb startup text in selftest.exp

Atm selftest.exp fails for me.

One of the reasons is that in c61b06a19a34baab66e3809c7b41b0c31009ed9f (Remove
some text from --version output) an eol was added after "There is NO
WARRANTY, to the extent permitted by law".

This patch updates the matching of the gdb startup message in selftest.exp
accordingly.

Tested selftest.exp (with two other selftest.exp related fixes applied).

2018-06-12  Tom de Vries  <tdevries@suse.de>

	* gdb.gdb/selftest.exp (test_with_self): Update gdb startup text.