Android: Enable C99 mode instead of C89 (default).

webrtc/BUILD.gn

Index: webrtc/BUILD.gn
diff --git a/webrtc/BUILD.gn b/webrtc/BUILD.gn
index 40368597b22dc5cab2ef3215c8d6bd8159defd64..56d06cf1291d66684004a03dc4441a967f9b014a 100644
--- a/webrtc/BUILD.gn
+++ b/webrtc/BUILD.gn
@@ -154,14 +154,18 @@ config("common_config") {
   }
 
   if (is_android && !is_clang) {
-    # The Android NDK doesn"t provide optimized versions of these
-    # functions. Ensure they are disabled for all compilers.
     cflags += [
+      # The Android NDK doesn't provide optimized versions of these
+      # functions. Ensure they are disabled for all compilers.
       "-fno-builtin-cos",
       "-fno-builtin-sin",
       "-fno-builtin-cosf",
       "-fno-builtin-sinf",
     ]
+    cflags_c = [
+      # Use C99 mode instead of C89 (default).
+      "-std=c99",
+    ]
   }
 }