Use std:: on symbols declared in C++-style C headers.

Some libraries (e.g. Dinkumware) perform strict checks on whether
the symbols defined in classic C library headers (e.g. <stdio.h>),
or in C++-style C library headers (e.g. <cmath>) are used correctly
(respectively, in the global namespace, or in namespace std).

BUG=
R=danno@chromium.org

Review URL: https://codereview.chromium.org/121303005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18578 ce2b1a6d-e550-0410-aec6-3dcde31c8c00