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_exit.cpp b/libc/bionic/pthread_exit.cpp
index 2692762..de818cd 100644
--- a/libc/bionic/pthread_exit.cpp
+++ b/libc/bionic/pthread_exit.cpp
@@ -92,7 +92,7 @@
   size_t stack_size = thread->attr.stack_size;
   bool user_allocated_stack = ((thread->attr.flags & PTHREAD_ATTR_FLAG_USER_ALLOCATED_STACK) != 0);
 
-  pthread_mutex_lock(&gThreadListLock);
+  pthread_mutex_lock(&g_thread_list_lock);
   if ((thread->attr.flags & PTHREAD_ATTR_FLAG_DETACHED) != 0) {
     // The thread is detached, so we can free the pthread_internal_t.
     // First make sure that the kernel does not try to clear the tid field
@@ -110,7 +110,7 @@
     // pthread_join is responsible for destroying the pthread_internal_t for non-detached threads.
     // The kernel will futex_wake on the pthread_internal_t::tid field to wake pthread_join.
   }
-  pthread_mutex_unlock(&gThreadListLock);
+  pthread_mutex_unlock(&g_thread_list_lock);
 
   if (user_allocated_stack) {
     // Cleaning up this thread's stack is the creator's responsibility, not ours.