cmake: mark WinMain as an undefined symbol, when building with mingw

cmake/win/WinFunctions.cmake

@@ -4,4 +4,17 @@ set(GLFW3_STATIC_INIT ON)
 set(LIBRW_STATIC_RUNTIME_DEFAULT ON)
 
 function(librw_platform_target TARGET)
+    cmake_parse_arguments(LPT "PROVIDES_WINMAIN" "" "" ${ARGN})
+    get_target_property(TARGET_TYPE "${TARGET}" TYPE)
+
+    if(MINGW)
+        if(LPT_PROVIDES_WINMAIN AND TARGET_TYPE MATCHES "^(INTERFACE|SHARED|STATIC)_LIBRARY$")
+            # Start with the WinMain symbol marked as undefined.
+            # This will prevent the linker ignoring a WinMain symbol.
+            if(CMAKE_SIZEOF_VOID_P EQUAL 4)
+                target_link_options(${TARGET} INTERFACE -Wl,--undefined,_WinMain@16)
+            endif()
+            target_link_options(${TARGET} INTERFACE -Wl,--undefined,WinMain)
+        endif()
+    endif()
 endfunction()

skeleton/CMakeLists.txt

@@ -31,17 +31,19 @@ set_target_properties(librw_skeleton
         EXPORT_NAME skeleton
 )
 
-target_link_libraries(librw_skeleton
-    PRIVATE
-        librw
-)
-
 target_include_directories(librw_skeleton
     PUBLIC
         $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>
         $<INSTALL_INTERFACE:${LIBRW_INSTALL_INCLUDEDIR}/skeleton>
 )
 
+target_link_libraries(librw_skeleton
+    PRIVATE
+        librw
+)
+
+librw_platform_target(librw_skeleton PROVIDES_WINMAIN INSTALL)
+
 if(LIBRW_INSTALL)
     install(
         FILES

src/CMakeLists.txt

@@ -192,6 +192,8 @@ elseif(LIBRW_PLATFORM_D3D9)
     )
 endif()
 
+librw_platform_target(librw INSTALL)
+
 if(LIBRW_INSTALL)
     install(
         FILES