[Windows] Identify proper run environment for scripts.
https://bugs.webkit.org/show_bug.cgi?id=116114

Reviewed by David Kilzer.

Determine (based on Visual Studio version) which path to use for
executables (bin versus bin32).

* Scripts/webkitdirs.pm:
(determineVisualStudioInstallDir): Added.
(determineVisualStudioVersion): Added.
(determineConfigurationProductDir): Modified to choose proper bin
or bin32 directory.
(visualStudioVersion): Added
(setupCygwinEnv): Modified to use new determineVisualStudioInstallDir


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@150092 268f45cc-cd09-0410-ab3c-d52691b4dbfc