Explicitly include "llvm/Support/MemoryBuffer.h" for MemoryBufferRef
Explicitly include "llvm/Support/MemoryBuffer.h" for MemoryBufferRef

Without this, this upstream LLVM commit b9a15c245f2 will break the
build.

GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc,GPUOpen-Drivers/llpc,googlestadia/llpc,googlestadia/llpc,googlestadia/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc,googlestadia/llpc,GPUOpen-Drivers/llpc