e8b9f2d7 introduced a different cast which broke building on Illumos.
Revert to previous behavior for V8_OS_SOLARIS only.

Found on SmartOS while building with gcc 4.9.0.

edit1: adding jochen to reviewers since he was assigned through the issue tracker and danno since he seems to do a fair amount of cross-platform work

edit2: removing BUG reference because I don't understand what LOG needs to contain (and it seems to link to chromium and not the v8 repo). Please edit commit message as appropriate.

BUG=3935
LOG=n

Review URL: https://codereview.chromium.org/990063002

Cr-Commit-Position: refs/heads/master@{#27163}