build: Add msgpack as git submodule

.gitmodules

@@ -4,3 +4,6 @@
 [submodule "src/xswiftbus/xplanemp2"]
 	path = src/xswiftbus/xplanemp2
 	url = git@github.com:swift-project/xplanemp2.git
+[submodule "third_party/msgpack"]
+	path = third_party/msgpack
+	url = https://github.com/msgpack/msgpack-c.git

CMakeLists.txt

@@ -143,7 +143,6 @@ endif()
 add_subdirectory(cmake/vatsimauth)
 add_subdirectory(cmake/dbus)
 add_subdirectory(cmake/sodium)
-add_subdirectory(cmake/msgpack)
 add_subdirectory(cmake/rapidjson)
 add_subdirectory(cmake/opus)
 add_subdirectory(cmake/crashpad)

cmake/msgpack/CMakeLists.txt

@@ -1,5 +0,0 @@
-# SPDX-FileCopyrightText: Copyright (C) swift Project Community / Contributors
-# SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-swift-pilot-client-1
-
-add_library(externals_msgpack INTERFACE)
-target_include_directories(externals_msgpack INTERFACE ${PROJECT_SOURCE_DIR}/third_party/externals/common/include)

src/blackcore/CMakeLists.txt

@@ -255,7 +255,7 @@ target_link_libraries(core
             input
             sound
             externals_sodium
-            externals_msgpack
+            msgpack-cxx
             blackconfig
         PRIVATE
             Qt::Qml

third_party/CMakeLists.txt

@@ -3,3 +3,4 @@
 
 add_subdirectory(simplecrypt)
 add_subdirectory(qjsonwebtoken)
+add_subdirectory(cmake/msgpack EXCLUDE_FROM_ALL SYSTEM)

third_party/cmake/msgpack/CMakeLists.txt

@@ -0,0 +1,12 @@
+# SPDX-FileCopyrightText: Copyright (C) swift Project Community / Contributors
+# SPDX-License-Identifier: GPL-3.0-or-later OR LicenseRef-swift-pilot-client-1
+
+# for simplicity, we are using our own CMake file to provide the msgpack-cxx target
+
+add_library(msgpack-cxx INTERFACE)
+
+if(NOT EXISTS ${PROJECT_SOURCE_DIR}/third_party/msgpack/include/)
+    message(FATAL_ERROR "msgpack not found. Did you forget to initialize the git submodules?")
+endif()
+
+target_include_directories(msgpack-cxx INTERFACE ${PROJECT_SOURCE_DIR}/third_party/msgpack/include)