BaseTools/tools_def: add CLANG38 LTO versions for AARCH64 and ARM

BaseTools/tools_def: add CLANG38 LTO versions for AARCH64 and ARM

Extend the CLANG38 toolchain definition so it can be used for
ARM and AARCH64 as well. Note that this requires llvm-ar and
the LLVMgold.so linker plugin.

In preparation of doing the same for GCC5, this toolchain version
also departs from the custom of using -O0 for DEBUG builds, which
makes them needlessly slow. Instead, let's add a NOOPT flavor as
well, and enable optimization for DEBUG like the other architectures
do. (Note that this will require some trivial changes to the platform
description files)

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Acked-by: Laszlo Ersek <lersek@redhat.com>
Tested-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Liming Gao <liming.gao@intel.com>