stm32/Makefile: Quote libgcc path so spaces are not an issue.
stm32/Makefile: Quote libgcc path so spaces are not an issue.

Fixes #3116.

adafruit/circuitpython,henriknelson/micropython,pramasoul/micropython,bvernoux/micropython,selste/micropython,MrSurly/micropython,bvernoux/micropython,adafruit/circuitpython,adafruit/circuitpython,kerneltask/micropython,selste/micropython,bvernoux/micropython,MrSurly/micropython,adafruit/circuitpython,henriknelson/micropython,henriknelson/micropython,pramasoul/micropython,kerneltask/micropython,pramasoul/micropython,kerneltask/micropython,bvernoux/micropython,henriknelson/micropython,pramasoul/micropython,selste/micropython,selste/micropython,kerneltask/micropython,bvernoux/micropython,adafruit/circuitpython,kerneltask/micropython,adafruit/circuitpython,MrSurly/micropython,selste/micropython,henriknelson/micropython,MrSurly/micropython,pramasoul/micropython,MrSurly/micropython