libart: Force SaberMod GCC 4.8 on ARM.

GCC 4.9 causes ridiculous segfaults on at least ARM targets for ART.

Change-Id: I878e95e2fe88f7fbfb2ca6c75202a3c699e0fc84
Increase default allocation stack size

Prevents some GC for alloc which can occur if the allocation stack
overflows.

Bug: 18707404

(cherry picked from commit 4911153db37264de407b2a08c2e4c9bb6aef3545)

Change-Id: I4748485dd495526ab1a313f366d93dbb3ee8112b