Update GCC 10 for Unicode (non-ASCII) identifiers support

[liuxilu]

GCC 10 Changes

Extended characters in identifiers may now be specified directly in the input encoding (UTF-8, by default), in addition to the UCN syntax (\uNNNN or \UNNNNNNNN) that is already supported:
static const int π = 3;
int get_naïve_pi() {
return π;
}

I tried this and it worked:
https://github.com/ZakKemble/avr-gcc-build/releases/tag/v14.1.0-1