Fix gunit compilation on VS2012.

In VS2012 compiling gunit or its dependencies triggers a lot of
"'std::tuple' : too many template arguments" warnings. The workaround
for this, done for gtest already, is to define _VARIADIC_MAX=10.

BUG=2616
R=perkj@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/8089004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5493 4adac7df-926f-26a2-2b94-8c16560cd09d

talk/libjingle_tests.gyp

@@ -39,7 +39,11 @@
         '<(DEPTH)/testing/gtest/include',
         '<(DEPTH)/testing/gtest',
       ],
+      'defines': ['_VARIADIC_MAX=10'],
       'direct_dependent_settings': {
+        'defines': [
+          '_VARIADIC_MAX=10',
+        ],
         'include_dirs': [
           '<(DEPTH)/testing/gtest/include',
         ],