_B and _C fields collide with esp-idf's newlib's ctype.h

[Andrii Neverov]

https://github.com/espressif/esp-idf/blob/master/components/newlib/include/ctype.h has

#define _C 040
...
#define _B 0200

Changing to something like _b/_c or _PIN_B/_PIN_C solves the issue.