Disabled the -Wextra warning as resolve the warnings will create other warnings under other compilers

src/osgViewer/CMakeLists.txt

@@ -7,8 +7,18 @@ ENDIF()
 
 SET(LIB_NAME osgViewer)
 
+
+################################################################################
+## Quieten warnings that a due to optional code paths
+
+IF(CMAKE_COMPILER_IS_GNUCXX)
+    # Remove -Wextra flag as it barfs on ffmoeg headers
+   STRING(REGEX REPLACE "-Wextra" "" CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS}")
+ENDIF()
+
 SET(HEADER_PATH ${OpenSceneGraph_SOURCE_DIR}/include/${LIB_NAME})
 
+
 FILE(GLOB CONFIG_HEADER_FILES ${HEADER_PATH}/config/*)
 FILE(GLOB CONFIG_SOURCE_FILES config/*.cpp)