gdb.base/gnu_vector.exp: Don't test output from the inferior

gdb.base/gnu_vector.exp: Don't test output from the inferior

gdb.base/gnu_vector.c printf the vector and gdb.base/gnu_vector.exp
expects the output by gdb_test_multiple.  Nowadays, the test doesn't
expect the output from inferior_spawn_id, which is wrong.  Even we
change the test to expect from inferior_spawn_id for the inferior
output, it is still possible the inferior exit before tcl/expect gets
the inferior output.  We see this fail on both s390x-linux and
ppc-linux on buildbot,

  FAIL: gdb.base/gnu_vector.exp: verify vector return value (the program exited)

https://sourceware.org/ml/gdb-testers/2015-q4/msg04922.html
https://sourceware.org/ml/gdb-testers/2015-q4/msg04952.html

In order to address these two shortcomings above in gnu_vector.exp,
this patch rewrites the test a little bit.  Get rid of checking the
inferior output, and instead checking them by printing them.  In this
way, the test can also be run on the target without inferior io
(gdb,noinferiorio is set in the board file).

gdb/testsuite:

2015-11-13  Yao Qi  <yao.qi@linaro.org>

	* gdb.base/gnu_vector.exp: Check the return value by "p res".
	* gdb.base/gnu_vector.c: Don't include stdio.h.
	(main): Don't print res and call add_some_intvecs.