[clang] [llvm] [PowerPC] Take ABI into account for data layout (PR #149725)

[Alex Rønne Petersen via cfe-commits]

alexrp wrote:

The only Linux distro I can find that actually claims support for `powerpc64` + `elfv2` + glibc is [Void](https://voidlinux-ppc.org):

> Void-ppc uses a variant of the modern ELFv2 ABI (loosened not to impose the POWER8/VSX requirements of the specification) on 64-bit glibc, as the only distribution known to do so.

... but that's not really ELFv2 then, is it? If that ABI variant is what this PR is actually about, then it seems to me that a new name should be created for this to avoid confusion. (`elfv2g5` or something? :shrug:)

https://github.com/llvm/llvm-project/pull/149725