[AArch64] PR18668, repair long branch veneer for plt stub

[AArch64] PR18668, repair long branch veneer for plt stub

2015-08-11  Jiong Wang  <jiong.wang@arm.com>
bfd/
   PR ld/18668
   * elfnn-aarch64.c (aarch64_type_of_stub): Update destination for
   calls go through plt stub.
   (elfNN_aarch64_final_link_relocate): Adjust code logic for CALL26,
   JUMP26 relocation to support inserting veneer for call to plt stub.

ld/testsuite/
   * ld-aarch64/farcall-b-gsym.s: New test.
   * ld-aarch64/farcall-b-plt.s: Likewise.
   * ld-aarch64/farcall-bl-plt.s: Likewise.
   * ld-aarch64/farcall-b-gsym.d: New expect file.
   * ld-aarch64/farcall-b-plt.d: Likewise.
   * ld-aarch64/farcall-bl-plt.d: Likewise.