Added new map.cc file to Bazel BUILD file.

Author: haberman

BUILD

@@ -175,6 +175,7 @@ cc_library(
         "src/google/protobuf/io/zero_copy_stream.cc",
         "src/google/protobuf/io/zero_copy_stream_impl.cc",
         "src/google/protobuf/io/zero_copy_stream_impl_lite.cc",
+        "src/google/protobuf/map.cc",
         "src/google/protobuf/message_lite.cc",
         "src/google/protobuf/parse_context.cc",
         "src/google/protobuf/repeated_field.cc",