Merged r16772, r18000, r18030, r18298, r18319 into 3.21 branch.

Merged r16772, r18000, r18030, r18298, r18319 into 3.21 branch.

Add a mechanism to override the detected cpu features.

Restore saved caller FP registers on stub failure and preserve FP registers on NotifyStubFailure.

MIPS: Fix and simplify code aging.

Initialize Date parse cache with SMI instead of double to workaround sharing mutable heap numbers in snapshot.

Fix NotifyStubFailureSaveDoubles generation for ia32.

BUG=280531
LOG=N
R=svenpanne@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=18552

[Sven Panne, 2014-01-13 09:23:47]

LGTM (rubberstamped)

[ulan, 2014-01-13 09:56:47]

Committed patchset #1 manually as r18552 (presubmit successful).