Halide_BUNDLE_LLVM doesn't work with universal builds on OSX

[derek-gerstmann]

It appears that bundle_static() in dependencies\llvm\CMakeLists.txt:140 is only injecting the arm64 libs from a universal build of LLVM, when Halide is also configured as a universal build (via CMAKE_OSX_ARCHITECTURES="x86_64;arm64").

The LLVM x86_64 libs are not getting bundled, resulting in missing symbols that show up when linking against libHalide.a:

Undefined symbols for architecture x86_64:
"_LLVMInitializeAArch64AsmParser", 
"..."

I'm not entirely sure why only the arm64 libs get bundled. Is the llvm_map_components_to_libnames provided with the LLVM project skipping them?

[derek-gerstmann]

@alexreinking Any thoughts?