Use cmake-scripts to manage gtest dependency

.gitmodules

@@ -70,12 +70,12 @@
 [submodule "lib/CImg"]
 	path = lib/CImg
 	url = https://github.com/dtschump/CImg.git
-[submodule "lib/googletest"]
-	path = lib/googletest
-	url = https://github.com/google/googletest
 [submodule "lib/boost-container"]
 	path = lib/boost-container
 	url = https://github.com/boostorg/container
 [submodule "lib/linuxdeploy-desktopfile"]
 	path = lib/linuxdeploy-desktopfile
 	url = https://github.com/linuxdeploy/linuxdeploy-desktopfile
+[submodule "lib/cmake-scripts"]
+	path = lib/cmake-scripts
+	url = https://github.com/linuxdeploy/cmake-scripts.git

CMakeLists.txt

@@ -43,11 +43,17 @@ if(ENABLE_COVERAGE)
     setup_target_for_coverage_gcovr_text(NAME coverage_text EXECUTABLE "${command}")
 endif()
 
+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

@@ -51,7 +51,3 @@ if(NOT USE_SYSTEM_BOOST)
         boost_type_traits boost_static_assert boost_integer boost_preprocessor boost_functional boost_detail
     )
 endif()
-
-if(BUILD_TESTING AND NOT TARGET gtest)
-    add_subdirectory(googletest)
-endif()

lib/cmake-scripts

@@ -0,0 +1 @@
+Subproject commit 21bd317812e44f7ed925f3f3bffcb7136c30ae74

lib/googletest

@@ -1 +0,0 @@
-Subproject commit 3bb00b7ead35ca3a9b5817ce1ab78050fe6be0e3

lib/linuxdeploy-desktopfile

@@ -1 +1 @@
-Subproject commit 25c0b0aa98235b2cbce25fd48ea3dc882554ca47
+Subproject commit f17d6bc562b433546dfcfc2c9456a752167fbe17