ci: build fewer LLVM components

This is a recommendation from WebAssembly#304 to build less of LLVM in CI. Perhaps
it can speed up build times.

Makefile

@@ -65,6 +65,10 @@ build/llvm.BUILT:
 		-DCMAKE_OSX_ARCHITECTURES="arm64;x86_64" \
 		-DCMAKE_OSX_DEPLOYMENT_TARGET=10.12 \
 		-DCMAKE_INSTALL_PREFIX=$(PREFIX) \
+		-DLLVM_INCLUDE_TESTS=OFF \
+		-DLLVM_INCLUDE_UTILS=OFF \
+		-DLLVM_INCLUDE_BENCHMARKS=OFF \
+		-DLLVM_INCLUDE_EXAMPLES=OFF \
 		-DLLVM_TARGETS_TO_BUILD=WebAssembly \
 		-DLLVM_DEFAULT_TARGET_TRIPLE=wasm32-wasi \
 		-DLLVM_ENABLE_PROJECTS="lld;clang;clang-tools-extra" \