Don't rely on inferior I/O in gdb.base/siginfo-addr.exp

Don't rely on inferior I/O in gdb.base/siginfo-addr.exp

No point in relying on stdio in this test.  Simply run to a breakpoint
instead.

gdb/testsuite/ChangeLog:
2015-07-29  Pedro Alves  <palves@redhat.com>

	* gdb.base/siginfo-addr.c (pass): New function.
	(handler): Call it iff si_addr is correct.
	* gdb.base/siginfo-addr.exp: Remove gdb_skip_stdio_test check.
	Set a breakpoint at "pass" and continue to it.