fix compiler warning for matrixportal buildenv

Author: softhack007

platformio.ini

@@ -2487,6 +2487,7 @@ board_build.f_flash = 80000000L
 board_build.flash_mode = qio
 
 build_unflags = ${env:esp32S3_8MB_M.build_unflags}   ;; use the same as "normal" S3 buildenv
+  -D ARDUINO_USB_CDC_ON_BOOT=1                       ;; fix warning: "ARDUINO_USB_CDC_ON_BOOT" redefined; comment out for Serial debug
 build_flags = ${common.build_flags} ${esp32s3.build_flags} -Wno-misleading-indentation -Wno-format-truncation
   ${common_mm.build_flags_S}
   -D WLED_RELEASE_NAME=matrixportal_esp32s3