Move gettid() into libcutils.

Change-Id: Ic8a15036833e6d129b7998d954b804be391de399
diff --git a/include/cutils/threads.h b/include/cutils/threads.h
index ade9a0c..bb9fdb8 100644
--- a/include/cutils/threads.h
+++ b/include/cutils/threads.h
@@ -37,9 +37,10 @@
     pthread_mutex_t   lock;
     int               has_tls;
     pthread_key_t     tls;
-
 } thread_store_t;
 
+extern pid_t gettid();
+
 #define  THREAD_STORE_INITIALIZER  { PTHREAD_MUTEX_INITIALIZER, 0, 0 }
 
 #else // !defined(_WIN32)
@@ -51,7 +52,6 @@
     int               has_tls;
     DWORD             tls;
     CRITICAL_SECTION  lock;
-
 } thread_store_t;
 
 #define  THREAD_STORE_INITIALIZER  { 0, 0, 0, {0, 0, 0, 0, 0, 0} }