This updates LLVMReactor to provide for PPC64 little endian support. It
also adds an #ifdef condition to an assert macro, since
llvm::sys::getHostCPUFeatures will always return false on non-x86 and
ARM Linux platforms per
'third_party/llvm-7.0/llvm/lib/Support/Host.cpp'.

Bug: b/135175069
Signed-off-by: Colin Samples <colin.samples+git@gmail.com>
Change-Id: Idcdafe2f1bd934317ca9da09c99132f814fcf160
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/32811
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>