linux: use CLOCK_{REALTIME,MONOTONIC}_COARSE

linux: use CLOCK_{REALTIME,MONOTONIC}_COARSE

R=bmeurer@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=17642

[bnoordhuis, 2013-11-11 13:54:57]

Use CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE when available for reasons
of being faster than the traditional gettimeofday() and
clock_gettime(CLOCK_MONOTONIC) system calls.

As mentioned in CR 51333007, I can change the guard logic to `#if
defined(CLOCK_REALTIME_COARSE)` and `#if defined(CLOCK_MONOTONIC_COARSE)` so
Android gets it for free if/when they add support for it.

[Benedikt Meurer, 2013-11-12 12:16:49]

On 2013/11/11 13:54:57, bnoordhuis wrote:
> Use CLOCK_REALTIME_COARSE and CLOCK_MONOTONIC_COARSE when available for
reasons
> of being faster than the traditional gettimeofday() and
> clock_gettime(CLOCK_MONOTONIC) system calls.
> 
> As mentioned in CR 51333007, I can change the guard logic to `#if
> defined(CLOCK_REALTIME_COARSE)` and `#if defined(CLOCK_MONOTONIC_COARSE)` so
> Android gets it for free if/when they add support for it.

The problem is not Android itself, but the host toolchain. That's what the weird
V8_LIBRT_NOT_AVAILABLE macro is for. I updated the patch and did some minor
refactoring.

LGTM

[Benedikt Meurer, 2013-11-12 12:18:41]

Committed patchset #2 manually as r17642 (presubmit successful).