Require GTest to be provided by the system

Author: TheAssassin

.gitmodules

@@ -4,6 +4,3 @@
 [submodule "lib/args"]
 	path = lib/args
 	url = https://github.com/Taywee/args
-[submodule "lib/gtest"]
-	path = lib/gtest
-	url = https://github.com/google/googletest

lib/CMakeLists.txt

@@ -38,6 +38,6 @@ if(NOT USE_SYSTEM_ARGS)
 endif()
 
 # Google Test framework
-if(BUILD_TESTING AND NOT TARGET gtest)
-    add_subdirectory(gtest EXCLUDE_FROM_ALL)
+if(BUILD_TESTING AND NOT TARGET GTest::gtest)
+    find_package(GTest REQUIRED)
 endif()

lib/gtest

@@ -4,9 +4,9 @@ include(CTest)
 set(CMAKE_CXX_STANDARD 11)
 
 add_executable(test_zsutil test_zsutil.cpp)
-target_link_libraries(test_zsutil PRIVATE libzsync2 gtest cpr)
+target_link_libraries(test_zsutil PRIVATE libzsync2 GTest::gtest cpr)
 add_test(NAME test_zsutil COMMAND test_zsutil)
 
 add_executable(test_zshash test_zshash.cpp)
-target_link_libraries(test_zshash PRIVATE libzsync2 gtest cpr)
+target_link_libraries(test_zshash PRIVATE libzsync2 GTest::gtest cpr)
 add_test(NAME test_zshash COMMAND test_zshash)