Adds two tests, one fails and another passes. These tests illustrate
the way in which the ABI function gnuv3_pass_by_reference is
incomplete.

gdb/testsuite/ChangeLog:

2014-09-11  Siva Chandra Reddy  <sivachandra@google.com>

        PR c++/13403
        PR c++/15154
        * gdb.cp/non-trivial-retval.cc: New file.
        * gdb.cp/non-trivial-retval.exp: New file.