Add: unit test functionality using catch2

(cherry picked from commit 43a7e54067)

CMakeLists.txt

@@ -253,6 +253,7 @@ if(OPTION_PACKAGE_DEPENDENCIES)
     set(CMAKE_BUILD_WITH_INSTALL_RPATH ON)
 endif()
 
+include(CTest)
 include(SourceList)
 
 # Needed by rev.cpp
@@ -264,6 +265,9 @@ include(MSVCFilters)
 
 add_executable(openttd WIN32 ${GENERATED_SOURCE_FILES})
 set_target_properties(openttd PROPERTIES OUTPUT_NAME "${BINARY_NAME}")
+
+add_executable(openttd_test)
+set_target_properties(openttd_test PROPERTIES EXCLUDE_FROM_ALL TRUE)
 # All other files are added via target_sources()
 
 set(host_tools_list strgen settingsgen)
@@ -327,6 +331,9 @@ target_link_libraries(openttd
     openttd::binfiles
     Threads::Threads
 )
+target_link_libraries(openttd_test)
+include(Catch)
+catch_discover_tests(openttd_test)
 
 if(HAIKU)
     target_link_libraries(openttd "be" "network" "midi")