gdb/testsuite: Extend tests for print of cv qualifiers

This commit supplements whatis and ptype command tests for print of
const-volatile qualifiers.

gdb/testsuite/ChangeLog:
2021-11-16  Christina Schimpe  <christina.schimpe@intel.com>

	* gdb.cp/ptype-cv-cp.cc: New const and volatile typedef
	  variables.
	* gdb.cp/ptype-cv-cp.exp: Add new tests.