Update avr-libc to version 2.1.0 / rev 2 via SR 1035232
    
    https://build.opensuse.org/request/show/1035232
    by user rguenther + dimstar_suse
    - update to 2.1.0
      * Improvements and additions:
        - Patch #9187 improved the library coverage for the AVR_TINY
          architecture (ATtiny10 and relatives).  In particular, many
          of the functions from <string.h> are now available there.
    
        - Patch #8729 adds ISR_NOICF and ISR_FLATTEN to <avr/interrupt.h>
      * Bugs fixed:
        [#36933] Documentation no longer correctly describes how to declare
        [#41689] add static_assert to assert.h
        [#48898] power_usart3_* functions no more defined in power.h
        [#49020] dtostre() flags documentation error
        [#49447] Example code for uart_putchar() has error in recursive call
          strings for storage in program memory
        [#50439] avr/iom32u4.h does not define PRTIM4
        [#51755] iotn441.h & iotn841.h missing definitions for PUEA