Change define "ttgo-t-watch.build.board=T-Watch" to "ttgo-t-watch.build.board=T_Watch" prevent "warning: ISO C99 requires whitespace after the macro name"

[sweetlilmre]

The "-" in the board name causes a compiler warning when this is expanded to -DARDUINO_BOARD="T-Watch".
This pull request fixes those warnings by replacing the "-" with "_" and aligns with other board definitions.

[datacute]

@me-no-dev
Is it possible that the platformio builds are failing because platformio also needs to change the board definition, but platformio are waiting till this commit is merged? platformio/platform-espressif32#378

The build.board turns into a compile time define in the recipes in platform.txt e.g. in recipe.c.o.pattern
-DARDUINO_{build.board}
https://github.com/espressif/arduino-esp32/blob/master/platform.txt#L72

Defines are not allowed to have hyphens in their name.

T-Watch isn't the only board with an invalid build.board value

[me-no-dev]

already fixed in another commit