Previously, we expanded the behavior of DataLayout to allow representing
pointer sizes with an arbitrary number of bits, with the expectation
that most users would migrate to the getPointerSizeInBits API. We
implemented some backward compatibility for the getPointerSize() API to
return the minimum number of bytes needed to contain a poitner. However
it appears that there are some APIs, in particular, uses around Dwarf
Debug information where the pointer model is more constrained and
are expected to be a power 2.
This patch updates getPointerSize() in these cases return a power of
2 number of bytes. NFC for in-tree code since these architectures
already have a pointer size that is a power of 2.