Currently, ppc64le and ppc64 (defaulting to big endian) have the same descriptor, thus the linear scan always return ppc64le. Handle that through subtype. This is a recommit of f114f009486816ed4b3bf984f0fbbb8fc80914f6 with a new test setup that doesn't involves (unsupported) corefiles. Differential Revision: https://reviews.llvm.org/D124760