This fixes the following issues when cross compiling SwiftShader
for arm64 macOS using CMake:

- Sets architecture based on CMAKE_OSX_ARCHITECTURES settings.
- Add missing dependency to LLVM.
- Add a workaround for assembly file compilation on macOS in marl.

Bug: fix build
Test: cmake .. -DCMAKE_OSX_ARCHITECTURES=arm64

Change-Id: I8abba9e39907d8f4d59f51c57f09cd55d4edc148
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/51890
Kokoro-Result: kokoro <noreply+kokoro@google.com>
Tested-by: Yilong Li <liyl@google.com>
Commit-Queue: Yilong Li <liyl@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>