rs6000: Don't ICE when we disassemble an MMA variable [PR101322]

rs6000: Don't ICE when we disassemble an MMA variable [PR101322]

When we expand an MMA disassemble built-in with C++ using a pointer that
is cast to a valid MMA type, the type isn't passed down to the expand
machinery and we end up using the base type of the pointer which leads to
an ICE.  This patch enforces we always use the correct MMA type regardless
of the pointer type being used.

2022-08-31  Peter Bergner  <bergner@linux.ibm.com>

gcc/
	PR target/101322
	* config/rs6000/rs6000-builtin.cc (rs6000_gimple_fold_mma_builtin):
	Enforce the use of a valid MMA pointer type.

gcc/testsuite/
	PR target/101322
	* g++.target/powerpc/pr101322.C: New test.