c++: Treat OPAQUE_TYPE types as an aggregate type [PR97947]

c++: Treat OPAQUE_TYPE types as an aggregate type [PR97947]

MODE_OPAQUE and the associated OPAQUE_TYPE were added to stop the optimizers
from knowing how the bits in a variable with an opaque type are laid out.
This makes them a kind of pseudo aggregate type and we need to treat them
as such when we process the INIT initializer for variables with an
opaque type.

2020-12-02  Peter Bergner  <bergner@linux.ibm.com>

gcc/cp/
	PR c++/97947
	* typeck2.c (digest_init_r): Handle OPAQUE_TYPE as an aggregate type.

gcc/testsuite/
	PR c++/97947
	* g++.target/powerpc/pr97947.C: New test.