Disable PnaclDebugURLFlag* on windows.

Only really need to disable on 32-bit windows, but disable
on all for now. It uses debug stub which does not play
well with sandbox reservation on 32-bit.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=3765
TBR=bradnelson@chromium.org

Review URL: https://codereview.chromium.org/189993003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255535 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255535