In turbofan, after an addition operation where the same register is the
output and both inputs, if deoptimization is performed the input is
overwritten with the output value and the final result is not correct.
This is fixed by restoring the original value of the input before
deoptimization.

BUG=
TEST=mjsunit/regress/regress-int32-truncation

Review-Url: https://codereview.chromium.org/2102063002
Cr-Commit-Position: refs/heads/master@{#37524}