c++: prvalue of array type [PR111286]

Here we want to build a prvalue array to bind to the T reference, but we
were wrongly trying to strip cv-quals from the array prvalue, which should
be treated the same as a class prvalue.

	PR c++/111286

gcc/cp/ChangeLog:

	* tree.cc (rvalue): Don't drop cv-quals from an array.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/initlist-array22.C: New test.