[PowerPC] Add the LLVM triple for powerpcle [1/5]

[PowerPC] Add the LLVM triple for powerpcle [1/5]

Add a triple for powerpcle-*-*.

This is a little-endian encoding of the 32-bit PowerPC ABI, useful in certain niche situations:

1) A loader such as the FreeBSD loader which will be loading a little endian kernel. This is required for PowerPC64LE to load properly in pseries VMs.
Such a loader is implemented as a freestanding ELF32 LSB binary.

2) Userspace emulation of a 32-bit LE architecture such as x86 on 64-bit hosts such as PowerPC64LE with tools like box86 requires having a 32-bit LE toolchain and library set, as they operate by translating only the main binary and switching to native code when making library calls.

3) The Void Linux for PowerPC project is experimenting with running an entire powerpcle userland.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D93918