c++: extend Wdangling-reference17.C [PR109642]

This patch extends g++.dg/warn/Wdangling-reference17.C with code
from PR109642.  I'm not creating a new test because this one
already #includes the required headers.

	PR c++/109642

gcc/testsuite/ChangeLog:

	* g++.dg/warn/Wdangling-reference17.C: Additional testing.