ARM64: Preserve x8 and x9 when necessary.
Fix a couple of places were x8 and x9 are excluded from lists of saved
registers. These are caller-saved registers, so C code can corrupt them.
x8 and x9 were originally reserved for debug code in the ARM64 port, so
we didn't bother preserving them, but they are now normal allocatable
registers.
BUG=v8:3263
LOG=N
R=rmcilroy@chromium.org, ulan@chromium.org
Review URL: https://codereview.chromium.org/
233373002
git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@20658
ce2b1a6d-e550-0410-aec6-
3dcde31c8c00