Remove extra inclusion of pb_common.c and pb_decode.c, to avoid multiple symbol definitions. (#275)

* Remove extra inclusion of pb_common.c and pb_decode.c, to avoid
multiple symbol definitions.

* Add nanopb library as a link-time dependency.

Author: jonsimantov

remote_config/CMakeLists.txt

@@ -66,6 +66,11 @@ if (NOT PROTOBUF_FOUND)
 else()
   # Generates config.pb.c and config.pb.h
   NANOPB_GENERATE_CPP(PROTO_SRCS PROTO_HDRS src_protos/config.proto)
+  # Remove pb_common.c and pb_decode.c from PROTO_SRCS, as they are
+  # provided by Firebase App. Including them here causes symbols to
+  # have multiple definitions.
+  list(FILTER PROTO_SRCS EXCLUDE REGEX "/pb_.*\\.c")
+
   set(desktop_SRCS
       ${PROTO_SRCS}
       ${PROTO_HDRS}
@@ -111,6 +116,7 @@ else()
   set(additional_link_LIB
       firebase_rest_lib
       firebase_instance_id_desktop_impl
+      protobuf-nanopb-static
       flatbuffers)
 endif()