cmake: add USE_LTO option

CMakeLists.txt

@@ -9,6 +9,7 @@ option(APPIMAGE_UPDATER "Enables AppImage updater" OFF)
 option(DISCORD_RPC      "Enables Discord Rich Presence" ON)
 option(VRU              "Enables VRU support in RMG-Input" ON)
 option(USE_CCACHE       "Enables usage of ccache when ccache has been found" ON)
+option(USE_LTO          "Enables building with LTO/IPO when compiler supports it" ON)
 option(FORCE_XCB        "Forces Qt to use the xcb platform on linux" ${LINUX})
 option(NO_RUST          "Disables the building of rust subprojects" OFF)
 
@@ -32,6 +33,15 @@ if (USE_CCACHE)
     endif(CCACHE_FOUND)
 endif(USE_CCACHE)
 
+if (USE_LTO)
+    include(CheckIPOSupported)
+    check_ipo_supported(RESULT ENABLE_IPO)
+
+    if(ENABLE_IPO)
+        set(CMAKE_INTERPROCEDURAL_OPTIMIZATION ON)
+    endif(ENABLE_IPO)
+endif(USE_LTO)
+
 if (NOT PORTABLE_INSTALL AND (WIN32 OR MSYS))
     message(WARNING "Not-Portable build not supported on windows, re-enabling PORTABLE_INSTALL!")
     set(PORTABLE_INSTALL ON)

Source/RMG-Core/CMakeLists.txt

@@ -5,6 +5,12 @@ project(RMG-Core)
 
 set(CMAKE_CXX_STANDARD 20)
 
+# RMG-Core needs LTO disabled for windows
+# else linking fails
+if (WIN32)
+    set(CMAKE_INTERPROCEDURAL_OPTIMIZATION OFF)
+endif(WIN32)
+
 find_package(PkgConfig REQUIRED)
 pkg_check_modules(SDL2 REQUIRED sdl2)
 pkg_check_modules(MINIZIP REQUIRED minizip)