Don't add --output-def to EXTRA_LDFLAGS

CMakeLists.txt

@@ -1247,6 +1247,7 @@ ENDIF()
 SET_TARGET_PROPERTIES(OpenAL PROPERTIES VERSION ${LIB_VERSION}
                                         SOVERSION ${LIB_MAJOR_VERSION})
 SET_TARGET_PROPERTIES(OpenAL PROPERTIES OUTPUT_NAME ${LIBNAME})
+SET_PROPERTY(TARGET OpenAL APPEND_STRING PROPERTY LINK_FLAGS ${EXTRA_LDFLAGS})
 
 if(WIN32 AND NOT LIBTYPE STREQUAL "STATIC")
     SET_TARGET_PROPERTIES(OpenAL PROPERTIES PREFIX "")
@@ -1263,7 +1264,8 @@ if(WIN32 AND NOT LIBTYPE STREQUAL "STATIC")
                 MESSAGE(STATUS "WARNING: Cannot find dlltool, disabling .def/.lib generation")
             ENDIF()
         ELSE()
-            SET(EXTRA_LDFLAGS "${EXTRA_LDFLAGS} -Wl,--output-def,OpenAL32.def")
+            SET_PROPERTY(TARGET OpenAL APPEND_STRING PROPERTY LINK_FLAGS
+                         " -Wl,--output-def,OpenAL32.def")
             ADD_CUSTOM_COMMAND(TARGET OpenAL POST_BUILD
                 COMMAND "${SED_EXECUTABLE}" -i -e "s/ @[^ ]*//" OpenAL32.def
                 COMMAND "${DLLTOOL_EXECUTABLE}" -d OpenAL32.def -l OpenAL32.lib -D OpenAL32.dll
@@ -1274,7 +1276,6 @@ if(WIN32 AND NOT LIBTYPE STREQUAL "STATIC")
     ENDIF()
 ENDIF()
 
-SET_PROPERTY(TARGET OpenAL APPEND_STRING PROPERTY LINK_FLAGS ${EXTRA_LDFLAGS})
 TARGET_LINK_LIBRARIES(OpenAL ${EXTRA_LIBS})
 IF(TARGET build_version)
     ADD_DEPENDENCIES(OpenAL build_version)