py/py.mk: Don't hardcode path to libaxtls.a.
py/py.mk: Don't hardcode path to libaxtls.a.

Use -L$(BUILD), not -Lbuild. Otherwise, builds for different archs/subarchs
using different values of BUILD may fail.

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