Pass caller names to __pthread_internal_find for better errors.

On http://b/122082295 we had this abort:

  12-27 15:29:31.237 10222 10814 10848 F libc    : invalid pthread_t 0xb1907960 passed to libc

This wasn't super helpful. We can do better. Now you get something like
this instead:

  03-27 02:34:58.754 25329 25329 W libc    : invalid pthread_t (0) passed to pthread_join

Test: adb shell crasher
Bug: http://b/123255692
Change-Id: I1d545665a233308480cc3747ec3120e2b6de0453
diff --git a/libc/bionic/pthread_kill.cpp b/libc/bionic/pthread_kill.cpp
index 1531574..8b38f4c 100644
--- a/libc/bionic/pthread_kill.cpp
+++ b/libc/bionic/pthread_kill.cpp
@@ -35,7 +35,7 @@
 int pthread_kill(pthread_t t, int sig) {
   ErrnoRestorer errno_restorer;
 
-  pid_t tid = pthread_gettid_np(t);
+  pid_t tid = __pthread_internal_gettid(t, "pthread_kill");
 
   // tid gets reset to 0 on thread exit by CLONE_CHILD_CLEARTID.
   if (tid == 0 || tid == -1) return ESRCH;