message: cmake: remove shadow warnings for old GCC
  This should fix a weird warning thrown by gcc 4.8.3 compiling for armv6.
diff: @@ -28,6 +28,9 @@ else()
  if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
  + if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5)
  + set(warnings "${warnings} -Wno-shadow")
  + endif()
  if(CMAKE_CXX_COMPILER_VERSION VERSION_GREATER 6)
  set(warnings "${warnings} -Wduplicated-cond -Wnull-dereference")
  endif()
  