Update the toolchain

[Peque]

To newer versions of arm-none-eabi-gcc and arm-none-eabi-binutils.

Requirements:

• [ ] Generated binary must fit in the microcontroller (ideally not growing in size)
• [ ] Performance must not be affected significantly
• [ ] 1278df6f7cf3cd6a8f5ec541ba1210dc46afb3df should be reverted (see #416)
• [ ] libopencm3 should compile successfully for all families

[Peque]

Maybe the solution is to set the "specs":

LDFLAGS         += -specs=nano.specs
/* or */
TGT_LDFLAGS     += -specs=nano.specs

Should we use the TGT_ prefix?

Maybe related links:

• https://stackoverflow.com/questions/57963506/section-text-will-not-fit-after-upgrading-arm-none-eabi-gcc
• https://github.com/search?q=org%3Alibopencm3+nano&type=Code
• https://stackoverflow.com/questions/54042558/g-arm-none-eabi-upgrade-from-4-9-to-gcc-8-2-generated-binary-do-not-fit-any-m
• http://pabigot.github.io/bspacm/newlib.html

[Peque]

Have a look at:

• https://keithp.com/blogs/picolibc/
• https://github.com/keith-packard/picolibc

Update on picolibc (now Amazon is paying the developer): https://static.sched.com/hosted_files/osselc21/7b/picolibc.pdf