add build for protobuf-c
diff --git a/Makefile.am b/Makefile.am
index 43ca5b4..d39bda2 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -3,9 +3,12 @@
 
 all: grpc-c
 
+protobuf-c:
+	cd third_party/protobuf-c; ./autogen.sh; ./configure; make; sudo make install
+
 grpc:
 	cd third_party/grpc; git submodule update --init; make; sudo make install
 
-grpc-c: grpc
+grpc-c: grpc protobuf-c
 	cd third_party/grpc-c; autoreconf --install; git submodule update --init; ./configure
 	make -C third_party/grpc-c