Add workaround for aligned_alloc bug on AIX

Add workaround for aligned_alloc bug on AIX

20_util/memory_resource/2.cc FAILs on AIX 7.2.0.0, because aligned_alloc
incorrectly requires the alignment to be a multiple of sizeof(void*).

This adds a workaround to the operator new overload taking an alignment
value, to increase the alignment (and size) if needed.

	* libsupc++/new_opa.cc (operator new(size_t, align_val_t)): Add
	workaround for aligned_alloc bug on AIX.
	* testsuite/18_support/new_aligned.cc: New test.

From-SVN: r263073