Have the submodules working correctly.

client/glfwclient/CMakeLists.txt

@@ -0,0 +1,14 @@
+# Copyright (c) 2021 Dominic Msters
+# 
+# This software is released under the MIT License.
+# https://opensource.org/licenses/MIT
+
+file(GLOB_RECURSE SOURCES ${CMAKE_CURRENT_SOURCE_DIR}/*.c)
+file(GLOB_RECURSE HEADERS ${CMAKE_CURRENT_SOURCE_DIR}/*.h)
+add_executable(${PROJECT_NAME} ${SOURCES})
+
+target_link_libraries(${PROJECT_NAME} 
+  game
+  glfw
+  glad
+)