Avoid two SSP ABI's for AArch64.

[Carlos O'Donell]

Kumar, Marcus, Richard,

Is there any way we can avoid having two SSP ABI's for AArch64?

GCC discussion:
http://gcc.gnu.org/ml/gcc-patches/2013-11/msg02244.html

GLIBC question:
https://sourceware.org/ml/libc-help/2013-12/msg00000.html

Is it too late and the cat's out of the bag and we need to support,
test, and ensure both models worked intermixed?

All of this is under the assumption, and there is some data to back
this up via the pointer guard work, that on all AArch64's a TP+offset
access is always faster than loading the data from a global symbol.

Cheers,
Carlos.