This CL ensures that kRootRegister (ebx) is preserved in
BailoutOfDeoptimized and PopArgumentsAdaptorFrame.

This CL uses push/pop to preserve eax, even though it is not used in
OPTIMIZED_FUNCTION code. If we must get more performance, we might be
able to get rid of push/pop, but I've left it in because it is cleaner
code this way. Another alternative is to use ecx in case of embedded
builtins only (as it is used for speculation in the standard config).

Change-Id: I437c8754408414d82b2fbd8b33d2faeda17aee30
Bug: v8:6666
Reviewed-on: https://chromium-review.googlesource.com/1242886
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56195}