Fix definition of V8_LIBRT_NOT_AVAILABLE in v8.gyp since we test for it using #elif in time.cc.

Fix definition of V8_LIBRT_NOT_AVAILABLE in v8.gyp since we test for it using #elif in time.cc.

TBR=jkummerow@chromium.org

Committed: https://code.google.com/p/v8/source/detail?r=16460

[Benedikt Meurer, 2013-09-01 15:03:43]

Committed patchset #1 manually as r16460 (presubmit successful).

[Jakob Kummerow, 2013-09-02 12:00:45]

As discussed offline, this patch doesn't change anything, as defined values
default to 1 anyway. It doesn't hurt to keep it in for now, but the next cleanup
can take it out again.