Add test of V2 GNU build attribute notes.

	* testsuite/binutils-all/note-3-64.s: New test.  Checks assembly
	and decoding of version2 GNU build attribute notes.
	* testsuite/binutils-all/note-3-32.s: New test.  32-bit version of
	the above test.
	* testsuite/binutils-all/note-3-64.d: New test driver.
	* testsuite/binutils-all/note-3-32.d: New test driver.
	* testsuite/binutils-all/objcopy.exp: Run the new test.
	* readelf.c (is_64bit_abs_reloc): Add R_SPARC_64.