2. Add flag INTERNAL_LIBM to mpconfigboard.mk files to signal using lib/libm.
3. Fix floating-point warnings in lib/libm
4. Turn off -finline-limit, no longer needed due to 1.
5. Add explicit flags for SPI_FLASH_FILESYSTEM and INTERNAL_FLASH_FILESYSTEM
to mpconfigboard.mk files, so they don't need to know the name of the .c file
that implements those. Makefile takes care of checking the flags and including
the right files.
Everything works fine without USB being plugged in but faults (I think) when USB is plugged in. This is switched away from the USB code from the bootloader onto the USB code thats generated by Atmel Studio using the high level classes from ASF.