Fix CMP0065

This one definitely broke OpenMW when we bumped our minimum CMake version past 3.5, but that meant that we already knew about it and already knew how to fix it and which platforms were affected.

Author: AnyOldName3

CMakeModules/OsgMacroUtils.cmake

@@ -355,6 +355,14 @@ MACRO(SETUP_EXE IS_COMMANDLINE_APP)
         ENDIF()
     ENDIF()
 
+    IF(CMAKE_CXX_COMPILER_ID STREQUAL "Clang" AND DYNAMIC_OPENSCENEGRAPH)
+        # templated types used in OSG plugins and applications need to get the same type ID
+        # based on investigation for https://gitlab.com/OpenMW/openmw/-/issues/8039 by the OpenMW team, this is believed to only be necessary for Clang on Linux
+        # i.e. not for GCC anywhere, MSVC on Windows or for AppleClang on MacOS
+        # it's possible that this is really required by the C++ spec for all platforms and we're just getting away with it everywhere else
+        SET_TARGET_PROPERTIES(${TARGET_TARGETNAME} PROPERTIES ENABLE_EXPORTS ON)
+    ENDIF()
+
     SETUP_LINK_LIBRARIES()
 
 ENDMACRO(SETUP_EXE)

examples/osgCMakeExample/CMakeLists.txt

@@ -22,3 +22,11 @@ LINK_DIRECTORIES(${OSG_LIB_DIR})
 ADD_EXECUTABLE(${PROJECT_NAME} ${SOURCES})
 
 TARGET_LINK_LIBRARIES(${PROJECT_NAME} ${OSG_LIBRARIES} ${OSGVIEWER_LIBRARIES} ${OSGUTIL_LIBRARIES} ${OSGDB_LIBRARIES} ${OSGGA_LIBRARIES} ${OPENTHREADS_LIBRARIES})
+
+IF(CMAKE_CXX_COMPILER_ID STREQUAL "Clang")
+    # templated types used in OSG plugins and applications need to get the same type ID
+    # based on investigation for https://gitlab.com/OpenMW/openmw/-/issues/8039 by the OpenMW team, this is believed to only be necessary for Clang on Linux
+    # i.e. not for GCC anywhere, MSVC on Windows or for AppleClang on MacOS
+    # it's possible that this is really required by the C++ spec for all platforms and we're just getting away with it everywhere else
+    SET_TARGET_PROPERTIES(${TARGET_TARGETNAME} PROPERTIES ENABLE_EXPORTS ON)
+ENDIF()