Using FetchContent instead of submodules

CMakeLists.txt

@@ -58,6 +58,12 @@ if (${ENABLE_COVERAGE})
     list(APPEND LINKER_FLAGS gcov)
 endif ()
 
+fetchcontent_declare(
+        assimp
+        GIT_REPOSITORY https://github.com/assimp/assimp.git
+        GIT_TAG v6.0.3
+        GIT_SHALLOW ON
+)
 set(BUILD_SHARED_LIBS ON)
 set(ASSIMP_NO_EXPORT ON)
 set(ASSIMP_INSTALL OFF)
@@ -71,15 +77,21 @@ if (CMAKE_BUILD_TYPE STREQUAL "Debug")
 else ()
     set(ASSIMP_INJECT_DEBUG_POSTFIX OFF)
 endif ()
-add_subdirectory(external/assimp EXCLUDE_FROM_ALL)
+fetchcontent_makeavailable(assimp)
 
+fetchcontent_declare(
+        spdlog
+        GIT_REPOSITORY https://github.com/gabime/spdlog.git
+        GIT_TAG v1.17.0
+        GIT_SHALLOW ON
+)
 set(SPDLOG_ENABLE_PCH ON)
 set(SPDLOG_BUILD_WARNINGS ON)
 set(SPDLOG_PREVENT_CHILD_FD ON)
 set(SPDLOG_NO_THREAD_ID ON)
 set(SPDLOG_NO_TLS ON)
 set(SPDLOG_NO_ATOMIC_LEVELS ON)
-add_subdirectory(external/spdlog EXCLUDE_FROM_ALL)
+fetchcontent_makeavailable(spdlog)
 
 add_executable(LearnGtk4 main.cpp
         hello_world.cpp