Parallelize make in build.sh. (#371)

* parallelize build.sh make

* Encode in cmake the dependency of ray_redis_module on autogenerated flatbuffer files.

build.sh

@@ -32,5 +32,5 @@ pushd "$ROOT_DIR/python/ray/core"
     cmake -DCMAKE_BUILD_TYPE=Release ../../..
   fi
   make clean
-  make
+  make -j${PARALLEL}
 popd

src/common/CMakeLists.txt

@@ -37,6 +37,10 @@ add_custom_command(
   COMMENT "Running flatc compiler on ${COMMON_FBS_SRC}"
   VERBATIM)
 
+# Encode the fact that the ray redis module requires the autogenerated
+# flatbuffer files to compile.
+add_dependencies(ray_redis_module gen_common_fbs)
+
 add_dependencies(gen_common_fbs flatbuffers_ep)
 
 add_custom_target(