Disable warnings failing when using Clang on Windows.

This makes it possible to build WebRTC using Clang on Windows.
Depends on https://codereview.webrtc.org/1524703006/

BUG=webrtc:5360, webrtc:5366
NOTRY=True

Review URL: https://codereview.webrtc.org/1522223002

Cr-Commit-Position: refs/heads/master@{#11058}

webrtc/modules/audio_coding/codecs/isac/isac_test.gypi

@@ -25,6 +25,19 @@
         './main/test/simpleKenny.c',
         './main/util/utility.c',
       ],
+      'conditions': [
+        ['OS=="win" and clang==1', {
+          'msvs_settings': {
+            'VCCLCompilerTool': {
+              'AdditionalOptions': [
+                # Disable warnings failing when compiling with Clang on Windows.
+                # https://bugs.chromium.org/p/webrtc/issues/detail?id=5366
+                '-Wno-format',
+              ],
+            },
+          },
+        }],
+      ],  # conditions.
     },
     # ReleaseTest-API
     {
@@ -63,6 +76,5 @@
         './main/util/utility.c',
       ],
     },
-
   ],
 }