Fix rtc::CurrentThreadId() on Android

We have been using the Linux way of getting the thread id on Android,
even though we have a special code path for getting it on Android.

BUG=webrtc:8110

Review-Url: https://codereview.webrtc.org/3001333002
Cr-Original-Commit-Position: refs/heads/master@{#19494}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: d950d9eda1c970d87d0d67c1fd46f06735030438
diff --git a/rtc_base/platform_thread.cc b/rtc_base/platform_thread.cc
index f65743e..da5089a 100644
--- a/rtc_base/platform_thread.cc
+++ b/rtc_base/platform_thread.cc
@@ -29,10 +29,10 @@
 #elif defined(WEBRTC_POSIX)
 #if defined(WEBRTC_MAC) || defined(WEBRTC_IOS)
   ret = pthread_mach_thread_np(pthread_self());
-#elif defined(WEBRTC_LINUX)
-  ret =  syscall(__NR_gettid);
 #elif defined(WEBRTC_ANDROID)
   ret = gettid();
+#elif defined(WEBRTC_LINUX)
+  ret =  syscall(__NR_gettid);
 #else
   // Default implementation for nacl and solaris.
   ret = reinterpret_cast<pid_t>(pthread_self());