Use cmake-scripts to manage gtest dependency

Author: TheAssassin

.gitmodules

@@ -1,6 +1,6 @@
 [submodule "lib/linuxdeploy"]
 	path = lib/linuxdeploy
 	url = https://github.com/TheAssassin/linuxdeploy
-[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

@@ -6,10 +6,17 @@ include(CTest)
 set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
+include(CTest)
+
+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(lib)
+
 add_subdirectory(src)
 
-include(CTest)
 if(BUILD_TESTING)
     enable_testing()
     add_subdirectory(tests)

lib/CMakeLists.txt

@@ -1,7 +1,4 @@
 add_subdirectory(linuxdeploy EXCLUDE_FROM_ALL)
-if(NOT TARGET gtest AND BUILD_TESTING)
-    add_subdirectory(googletest EXCLUDE_FROM_ALL)
-endif()
 
 # required to properly build nlohmann/json v. 2.0.0 on trusty
 set(CMAKE_CXX_STANDARD 11)