Use cmake-scripts to manage gtest dependency

Author: TheAssassin

.gitmodules

@@ -1,3 +1,3 @@
-[submodule "lib/googletest"]
-	path = lib/googletest
-	url = https://github.com/google/googletest.git
+[submodule "lib/cmake-scripts"]
+	path = lib/cmake-scripts
+	url = https://github.com/linuxdeploy/cmake-scripts.git

CMakeLists.txt

@@ -46,7 +46,10 @@ endif()
 
 include(CTest)
 
-add_subdirectory(lib)
+if(BUILD_TESTING)
+    # including this before including lib/ makes sure that the top level project's gtest is used everywhere
+    include(${PROJECT_SOURCE_DIR}/lib/cmake-scripts/include-or-build-gtest.cmake)
+endif()
 
 add_subdirectory(src)