[CMake][PowerPC] Recognize LLVM_NATIVE_TARGET="ppc64le" as PowerPC
[CMake][PowerPC] Recognize LLVM_NATIVE_TARGET="ppc64le" as PowerPC

Summary:
This value is derived from the host triple, which on the machine
I'm currently using is `ppc64le-linux-redhat`. This change makes
LLVM compile.

Reviewers: nemanjai
Differential Revision: https://reviews.llvm.org/D57118

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@359242 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm