Add check for pthread_self() when looking up a thread

Check if thread_id is in fact pthread_self before
locking on g_thread_list_lock in __pthread_internal_find.

The main reason for doing this is not performance but to allow
the linker use raise() which was not working because pthread_kill()
couldn't find pthread_self() thread because the global thread
list is initialized in libc.so and the linker's version of this
list is empty.

Bug: http://b/25867917
Change-Id: I18fe620e8cd465b30f0e1ff45fff32958f3c5c00
diff --git a/libc/bionic/pthread_internal.cpp b/libc/bionic/pthread_internal.cpp
index 1967ccf..8946f79 100644
--- a/libc/bionic/pthread_internal.cpp
+++ b/libc/bionic/pthread_internal.cpp
@@ -81,6 +81,12 @@
 
 pthread_internal_t* __pthread_internal_find(pthread_t thread_id) {
   pthread_internal_t* thread = reinterpret_cast<pthread_internal_t*>(thread_id);
+
+  // check if thread is pthread_self() before acquiring the lock
+  if (thread == __get_thread()) {
+    return thread;
+  }
+
   ScopedPthreadMutexLocker locker(&g_thread_list_lock);
 
   for (pthread_internal_t* t = g_thread_list; t != NULL; t = t->next) {