toolchain-external: update Arm AArch64 toolchain 8.2-2018.11

toolchain-external: update Arm AArch64 toolchain 8.2-2018.11

>From [1]:
* All GCC 8.2 features. For details on GCC 8 release series.
* Linaro specific pre-processor macros to ensure that this is a
  continuation from the Linaro releases.
* Spectre v1 mitigation backport from upstream FSF trunk include the
  revisions. This is an initial backport of those mitigations in
  the GNU toolchain and should be regarded as support for prototyping
  and early access only. Moreover, while the backports include support
  for the other architectures, they are included for completeness and
  all issues regarding these patches must be taken up upstream in the
  https://gcc.gnu.org/bugzilla by reproducing the same with upstream
  FSF trunk.
  Arm is interested in feedback regarding these workarounds for
  Spectre v1.
  A description of the mitigation has been published on LWN.net.

See "Release Note":
[1] https://developer.arm.com/open-source/gnu-toolchain/gnu-a/downloads#

Tested with qemu_aarch64_virt_defconfig.

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>