bfd/elfnn-aarch64.c: Fix miscalculation of GOTPLT offset for ifunc syms.

bfd/elfnn-aarch64.c: Fix miscalculation of GOTPLT offset for ifunc syms.

The .got.plt header size was not being correctly taken into account
when calculating the offset for relocations against ifunc symbols.

bfd/ChangeLog:

2013-11-26  Will Newton  <will.newton@linaro.org>

	* elfnn-aarch64.c (elfNN_aarch64_final_link_relocate): Ensure
	PLT_INDEX is calculated using correct header size.

ld/testsuite/ChangeLog:

2013-11-26  Will Newton  <will.newton@linaro.org>

	* ld-aarch64/aarch64-elf.exp: Add ifunc-21 test.
	* ld-aarch64/ifunc-21.d: New file.
	* ld-aarch64/ifunc-21.s: Likewise.