[Win] Clean up some 64-bit warnings from Visual Studio analyzer

[Win] Clean up some 64-bit warnings from Visual Studio analyzer
https://bugs.webkit.org/show_bug.cgi?id=131514

Reviewed by Tim Horton.

* WTF.vcxproj/WTF.vcxproj: Use correct platform settings for
64-bit build.
* config.h: Ditto.
* wtf/CurrentTime.cpp:
(WTF::highResUpTime): Resolve warning about deprecated API.
* wtf/StackBounds.cpp:
(WTF::StackBounds::initialize): Silence warning about
an uninitialized variable.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@167101 268f45cc-cd09-0410-ab3c-d52691b4dbfc