Switch to g_ for globals.

That's what the Google style guide recommends, and we're starting
to get a mix.

Change-Id: Ib0c53a890bb5deed5c679e887541a715faea91fc
diff --git a/libc/bionic/pthread_key.cpp b/libc/bionic/pthread_key.cpp
index 6cc68af..27eab27 100644
--- a/libc/bionic/pthread_key.cpp
+++ b/libc/bionic/pthread_key.cpp
@@ -210,8 +210,8 @@
   }
 
   // Clear value in all threads.
-  pthread_mutex_lock(&gThreadListLock);
-  for (pthread_internal_t*  t = gThreadList; t != NULL; t = t->next) {
+  pthread_mutex_lock(&g_thread_list_lock);
+  for (pthread_internal_t*  t = g_thread_list; t != NULL; t = t->next) {
     // Skip zombie threads. They don't have a valid TLS area any more.
     // Similarly, it is possible to have t->tls == NULL for threads that
     // were just recently created through pthread_create() but whose
@@ -226,7 +226,7 @@
   }
   tls_map.DeleteKey(key);
 
-  pthread_mutex_unlock(&gThreadListLock);
+  pthread_mutex_unlock(&g_thread_list_lock);
   return 0;
 }