message: renderdoccmd: Use Android `d8` instead of `dx` dexer
  build-tools 31.0.0 doesn't ship with `dx` anymore, and Android Studio
  switched to `d8` back in April 2018 [1].
  The fallback for `dx` remains, in case older build-tools are used that
  do not support `d8` just yet.
  [1]:
diff: @@ -246,10 +246,17 @@ if(ANDROID)
  endif()
  endif()
  + set(D8_SCRIPT "${BUILD_TOOLS}/d8${TOOL_SCRIPT_EXTENSION}")
  + if(NOT EXISTS ${D8_SCRIPT})
  + set(DEX_COMMAND ${BUILD_TOOLS}/dx${TOOL_SCRIPT_EXTENSION} --dex --output=bin/classes.dex ./obj)
  + else()
  + set(DEX_COMMAND ${D8_SCRIPT} --output ./bin/ ./obj/org/renderdoc/renderdoccmd/*/*.class)
  + endif()
  +
  add_custom_command(OUTPUT ${APK_FILE} APPEND
  COMMAND ${BUILD_TOOLS}/aapt package -f -m -S res -J src -M AndroidManifest.xml -I ${ANDROID_JAR}
  COMMAND ${JAVA_BIN}/javac -d ./obj -source 1.7 -target 1.7 -bootclasspath ${RT_JAR} -classpath "${CLASS_PATH}" -sourcepath src src/org/renderdoc/renderdoccmd/*.java
  - COMMAND ${BUILD_TOOLS}/dx${TOOL_SCRIPT_EXTENSION} --dex --output=bin/classes.dex ./obj
  + COMMAND ${DEX_COMMAND}
  COMMAND ${BUILD_TOOLS}/aapt package -f -M AndroidManifest.xml --version-code ${APK_VERSION_CODE} --version-name ${APK_VERSION_NAME} -S res -I ${ANDROID_JAR} -F RenderDocCmd-unaligned.apk bin libs
  COMMAND ${BUILD_TOOLS}/zipalign -f 4 RenderDocCmd-unaligned.apk RenderDocCmd.apk
  COMMAND ${BUILD_TOOLS}/apksigner${TOOL_SCRIPT_EXTENSION} sign --ks ${KEYSTORE} --ks-pass pass:android --key-pass pass:android --ks-key-alias rdocandroidkey RenderDocCmd.apk
  