When relaxing, update symbols at the very end of the section.

When relaxing, update symbols at the very end of the section.

Symbols at the very end of a section were not being updated correctly
when linker relaxation takes place due to the use of '<' instead of
'<='.  Added a couple of tests to cover this behaviour.

bfd/ChangeLog:

	* elf32-avr.c (elf32_avr_relax_delete_bytes): Modify symbols
	located at the very end of the section.

ld/ChangeLog:

	* ld/testsuite/ld-avr/relax-02.d: New file.
	* ld/testsuite/ld-avr/relax-02.s: New file.
	* ld/testsuite/ld-avr/relax-03.d: New file.
	* ld/testsuite/ld-avr/relax-03.s: New file.