build env for -C3 with only 2MB flash

based on proposal from  in PR #2951 by @andyshinn.
2MB does not allow to have an OTA partition, so this feature is disabled.

platformio.ini

@@ -585,6 +585,24 @@ lib_deps = ${esp32s2.lib_deps}
 # custom board configurations
 # ------------------------------------------------------------------------------
 
+[env:esp32c3dev_2MB]
+;; for ESP32-C3 boards with 2MB flash (instead of 4MB).
+;; this board need a specific partition file. OTA not possible.
+extends = esp32c3
+platform = ${esp32c3.platform}
+platform_packages = ${esp32c3.platform_packages}
+board = esp32-c3-devkitm-1
+build_flags = ${common.build_flags} ${esp32c3.build_flags} #-D WLED_RELEASE_NAME=ESP32-C3
+  -D WLED_WATCHDOG_TIMEOUT=0
+  -D WLED_DISABLE_OTA
+  ; -DARDUINO_USB_CDC_ON_BOOT=1 ;; for virtual CDC USB
+  -DARDUINO_USB_CDC_ON_BOOT=0   ;; for serial-to-USB chip
+build_unflags = ${common.build_unflags}
+upload_speed = 115200
+lib_deps = ${esp32c3.lib_deps}
+board_build.partitions = tools/WLED_ESP32_2MB_noOTA.csv
+board_build.flash_mode = dio
+
 [env:wemos_shield_esp32]
 board = esp32dev
 platform = espressif32@3.2