Fix build error detection.
Set diy0.hex build dependencies.
Simplify MOTOR_REVERSE case.
Generalize diy0.hex build dependencies.
Add support for Hacker/Jeti Master 135-O-F5B boards (12MHz).
Fail if the given board define is not recognized.
Fix build regression for /bin/sh -> dash cases since 5a5792a96.

There seems to be no way to do the same as "set -o pipefail" in dash.
Remove safemode disabling from avrdude command line.
Remove broken / extraneous RCTimer 50A v2 target (use hk200a).

The B-phase high/low were flipped, and when corrected, it matches "hk200a".