Fix exception handling test on vs2010
Fix exception handling test on vs2010

Recently added exception handling test was getting optimized away on 2010
(confirmed by stepping through in debugger). I'm surprised it's allowed to
do so (since it clearly changes behaviour), but I guess that must be OK
according to "the rules" if it can prove there's always going to be a
divide by zero.

Anyway, avoid this by disabling optimizations.

R=thakis@chromium.org

Review URL: https://chromiumcodereview.appspot.com/9834097
witwall/gyp,witwall/gyp,witwall/gyp,witwall/gyp,witwall/gyp