[x64] Match -0 - x with sign bit flip.

[x64] Match -0 - x with sign bit flip.

We can use xorps/xorpd on Intel CPUs to flip the sign bit. Ideally we'd
use a RIP-relative 128-bit constant in the code object, as OCaml/GCC
does, however that requires 128-bit alignment for code objects, which is
not yet implemented. So for now we materialize the mask inline.

R=dcarney@chromium.org

Committed: https://crrev.com/a1b2c275b7c821d7569d247463f74968695903b4
Cr-Commit-Position: refs/heads/master@{#27611}

[Benedikt Meurer, 2015-03-30 11:32:48]

PTAL

[dcarney, 2015-03-30 11:38:47]

lgtm

[Benedikt Meurer, 2015-04-07 07:13:52]

The CQ bit was checked by bmeurer@chromium.org

[Benedikt Meurer, 2015-04-07 07:13:53]

The patchset sent to the CQ was uploaded after l-g-t-m from dcarney@chromium.org
Link to the patchset: https://codereview.chromium.org/1046893002/#ps20001
(title: "Unittest")

[commit-bot: I haz the power, 2015-04-07 07:13:58]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1046893002/20001

[commit-bot: I haz the power, 2015-04-07 07:35:01]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-07 07:35:19]

Patchset 2 (id:??) landed as
https://crrev.com/a1b2c275b7c821d7569d247463f74968695903b4
Cr-Commit-Position: refs/heads/master@{#27611}