use -flto instead of flto=auto for compilers other than GCC >= 12, as…

… per suggestion of Axel

CMakeLists.txt

@@ -51,8 +51,11 @@ add_compile_options(-Wall -Wextra -Wno-missing-field-initializers)
 add_compile_options(-DGTEST_HAS_TR1_TUPLE=0 -DGTEST_USE_OWN_TR1_TUPLE=0)
 
 # Basic optimization
-if(CMAKE_C_COMPILER_ID STREQUAL "GNU" AND CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 12)
+if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL 12)
 	add_compile_options(-flto=auto)
+else()
+	add_compile_options(-flto)
+	add_link_options(-flto)
 endif()
 
 add_compile_options(-march=native)