[x64] Fixed a rounding error on x64 for the Uint64ToF64 conversion.

[x64] Fixed a rounding error on x64 for the Uint64ToF64 conversion.

The least significant bit of the input value may affect the result of
the conversion through rounding. We OR the least significant with the
second least significant bit to preserve it over the SHR instruction.

R=titzer@chromium.org

Committed: https://crrev.com/71348aa2a07c0c3e2447a7b68296905e2bc3cf86
Cr-Commit-Position: refs/heads/master@{#31969}

[titzer, 2015-11-12 19:08:20]

On 2015/11/12 15:08:13, ahaas wrote:

lgtm

[ahaas, 2015-11-12 19:34:17]

The CQ bit was checked by ahaas@chromium.org

[commit-bot: I haz the power, 2015-11-12 19:34:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1435203003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1435203003/20001

[commit-bot: I haz the power, 2015-11-12 19:35:52]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-14 23:21:02]

Patchset 2 (id:??) landed as
https://crrev.com/71348aa2a07c0c3e2447a7b68296905e2bc3cf86
Cr-Commit-Position: refs/heads/master@{#31969}