disable bad gcc 6 warning

hw/bsp/family_support.cmake

@@ -113,6 +113,11 @@ if (NOT TARGET _family_support_marker)
             if (CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 8.0)
                 target_compile_options(${TARGET} PUBLIC -Wcast-function-type -Wstrict-overflow)
             endif()
+
+            # GCC 6
+            if (CMAKE_C_COMPILER_VERSION VERSION_GREATER_EQUAL 6.0)
+                target_compile_options(${TARGET} PUBLIC -Wno-strict-aliasing)
+            endif()
         endif()
     endfunction()
 

src/host/usbh.c

@@ -655,7 +655,9 @@ static bool usbh_control_xfer_cb (uint8_t dev_addr, uint8_t ep_addr, xfer_result
           TU_ASSERT( hcd_edpt_xfer(rhport, dev_addr, tu_edpt_addr(0, request->bmRequestType_bit.direction), _ctrl_xfer.buffer, request->wLength) );
           return true;
         }
+#if __GNUC__ >= 7
         __attribute__((fallthrough));
+#endif
 
       case CONTROL_STAGE_DATA:
         if (request->wLength)