[GTK] Change from PLATFORM(GTK) to USE(GLIB) in WTF/CurrentTime.cpp
https://bugs.webkit.org/show_bug.cgi?id=114061

Patch by Jesus Sanchez-Palencia <jesus.palencia@openbossa.org> on 2013-04-05
Reviewed by Gustavo Noronha Silva.

Now other ports using GLib can use the correct implementation
and not the fallback one without adding any other PLATFORM guards
here.

* wtf/CurrentTime.cpp:
(WTF):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147799 268f45cc-cd09-0410-ab3c-d52691b4dbfc