Non-ancient versions of the ARM-ARM explicitly deprecate most uses of the PC
within instructions and older ARM implementations have a non-predictable offset
(8 or 12) for some of these deprecated uses. Avoiding the deprecated instruction
costs us one additional instruction in DirectCEntryStub::GenerateCall, but this
should not cause any significant performance degradation.

The deoptimizer still uses the PC in a stm instruction, but it is a bit unclear
what to do about that, so simply a comment has been added to reconsider this in
the future.
Review URL: http://codereview.chromium.org/7633014

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@8916 ce2b1a6d-e550-0410-aec6-3dcde31c8c00