add a missing CMakeLists.txt (#98)

c++/CMakeLists.txt

@@ -0,0 +1,23 @@
+# Copyright 2023 Greptime Team
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may not
+# use this file except in compliance with the License. You may obtain a copy of
+# the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations under
+# the License.
+
+cmake_minimum_required(VERSION 3.22)
+
+project(greptime_proto_cpp_lib)
+
+file(GLOB_RECURSE OUTPUT_SOURCES "*.h" "*.cc")
+
+add_library(${PROJECT_NAME} ${OUTPUT_SOURCES})
+
+target_include_directories(${PROJECT_NAME} PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})