Make jni_helpers build on arm32.

talk/app/webrtc/java/jni/jni_helpers.cc

Index: talk/app/webrtc/java/jni/jni_helpers.cc
diff --git a/talk/app/webrtc/java/jni/jni_helpers.cc b/talk/app/webrtc/java/jni/jni_helpers.cc
index a2cbd61971ecdcb68d4f5913a92ae4ea56223136..b56af5d47f139d8bc12bb3c7568223dd6ca5b0e7 100644
--- a/talk/app/webrtc/java/jni/jni_helpers.cc
+++ b/talk/app/webrtc/java/jni/jni_helpers.cc
@@ -103,7 +103,8 @@ jint InitGlobalJniVariables(JavaVM *jvm) {
 // Return thread ID as a string.
 static std::string GetThreadId() {
   char buf[21];  // Big enough to hold a kuint64max plus terminating NULL.
-  CHECK_LT(snprintf(buf, sizeof(buf), "%ld", syscall(__NR_gettid)),
+  CHECK_LT(snprintf(buf, sizeof(buf), "%ld",
+           static_cast<long>(syscall(__NR_gettid))),
            sizeof(buf))
       << "Thread id is bigger than uint64??";
   return std::string(buf);