Build macOS universal binaries (#270)

Author: TerrorJack

Makefile

@@ -60,6 +60,8 @@ build/llvm.BUILT:
 		-DLLVM_ENABLE_ZLIB=OFF \
 		-DLLVM_ENABLE_ZSTD=OFF \
 		-DLLVM_STATIC_LINK_CXX_STDLIB=ON \
+		-DLLVM_HAVE_LIBXAR=OFF \
+		-DCMAKE_OSX_ARCHITECTURES="arm64;x86_64" \
 		-DCMAKE_INSTALL_PREFIX=$(PREFIX) \
 		-DLLVM_TARGETS_TO_BUILD=WebAssembly \
 		-DLLVM_DEFAULT_TARGET_TRIPLE=wasm32-wasi \