feat: c++17（最大）に変更

keke1008 · keke1008 · commit fb74dbee60f8 · 2023-05-13T17:48:51.000+09:00
c++20以降にしたいなら，以下が参考になる． arduino/ArduinoCore-avr#435 (comment)
diff --git a/platformio.ini b/platformio.ini
@@ -8,6 +8,10 @@
 ; Please visit documentation for the other options and examples
 ; https://docs.platformio.org/page/projectconf.html
 
+[env]
+build_unflags = -std=gnu++11
+build_flags = -std=gnu++17
+
 [env:megaatmega2560]
 platform = atmelavr
 board = megaatmega2560
