py/misc.h: Rename _MP_STRINGIFY to not use leading underscore in ident.
py/misc.h: Rename _MP_STRINGIFY to not use leading underscore in ident.

Macro identifiers with a leading underscore are reserved.

henriknelson/micropython,bvernoux/micropython,pozetroninc/micropython,selste/micropython,adafruit/circuitpython,trezor/micropython,adafruit/circuitpython,selste/micropython,kerneltask/micropython,pfalcon/micropython,kerneltask/micropython,trezor/micropython,trezor/micropython,adafruit/circuitpython,tobbad/micropython,bvernoux/micropython,kerneltask/micropython,pfalcon/micropython,pramasoul/micropython,adafruit/circuitpython,pramasoul/micropython,adafruit/circuitpython,pramasoul/micropython,MrSurly/micropython,MrSurly/micropython,kerneltask/micropython,bvernoux/micropython,pramasoul/micropython,henriknelson/micropython,tobbad/micropython,tobbad/micropython,pfalcon/micropython,pozetroninc/micropython,pozetroninc/micropython,henriknelson/micropython,pramasoul/micropython,MrSurly/micropython,tobbad/micropython,kerneltask/micropython,trezor/micropython,MrSurly/micropython,pozetroninc/micropython,MrSurly/micropython,bvernoux/micropython,selste/micropython,pozetroninc/micropython,pfalcon/micropython,selste/micropython,adafruit/circuitpython,henriknelson/micropython,pfalcon/micropython,bvernoux/micropython,tobbad/micropython,henriknelson/micropython,selste/micropython,trezor/micropython