Log Message:
cross/avr-libc: Update to 2.1.0

*** Changes in avr-libc-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[0-7] and PUEB[0-3]
  [no-id] util/eu_dst.h: fix reversed DST decision logic for March and October
  [no-id] util/delay.h.in: add missing return

* Contributed Patches:

  [no-id] Define weak symbols for known memory region sizes based on device.
          header definitions, starting with fuse region.
  [#8961] Update test script for new simulavr and library layout
  [#8964] Update tests isinf-01.c, signbit-01.c and modf-np.c
  [#9163] New eeprom write block function for xmega using eeprom page write
  [#8729] [avr/interrupt.h] Add ISR_NOICF, ISR_FLATTEN. Fix namespace of identifiers.
  [#8536] Fix a typo within <stdio.h>
  [#8649] small documentation fixes in
  [#9187] [AVR_TINY]: Support 16-bit xtoa functons and more string functions.
  [#9400] Add avrxmega3 multilibs
  [#9659] Update eeprom_is_ready for avrxmega3 devices
  [#9553] Fix some issues in libc/
  [#9864] Use proper float function names and prototypes