Remove libbacktrace definition of gettid.

Also simplifies the Darwin implementation of gettid, because
apparently libbacktrace had a better way of doing it.

Bug: 19517541

(cherry picked from commit 23f750b068)

Change-Id: I2f888e8ed7a2f5719973786cbcbb399a81867ee9

libbacktrace/Backtrace.cpp

@@ -27,6 +27,8 @@
 #include <backtrace/Backtrace.h>
 #include <backtrace/BacktraceMap.h>
 
+#include <cutils/threads.h>
+
 #include "BacktraceLog.h"
 #include "thread_utils.h"
 #include "UnwindCurrent.h"

libbacktrace/BacktraceCurrent.cpp

@@ -29,6 +29,8 @@
 #include <backtrace/Backtrace.h>
 #include <backtrace/BacktraceMap.h>
 
+#include <cutils/threads.h>
+
 #include "BacktraceCurrent.h"
 #include "BacktraceLog.h"
 #include "ThreadEntry.h"

libbacktrace/backtrace_test.cpp

@@ -30,20 +30,21 @@
 #include <time.h>
 #include <unistd.h>
 
-#include <backtrace/Backtrace.h>
-#include <backtrace/BacktraceMap.h>
-
-// For the THREAD_SIGNAL definition.
-#include "BacktraceCurrent.h"
-
-#include <cutils/atomic.h>
-#include <gtest/gtest.h>
-
 #include <algorithm>
 #include <memory>
 #include <string>
 #include <vector>
 
+#include <backtrace/Backtrace.h>
+#include <backtrace/BacktraceMap.h>
+
+#include <cutils/atomic.h>
+#include <cutils/threads.h>
+
+#include <gtest/gtest.h>
+
+// For the THREAD_SIGNAL definition.
+#include "BacktraceCurrent.h"
 #include "thread_utils.h"
 
 // Number of microseconds per milliseconds.

libbacktrace/thread_utils.c

@@ -16,25 +16,12 @@
 
 #include "thread_utils.h"
 
-#if defined(__APPLE__)
+#if !defined(__BIONIC__)
 
-#include <sys/syscall.h>
-
-// Mac OS >= 10.6 has a system call equivalent to Linux's gettid().
-pid_t gettid() {
-  return syscall(SYS_thread_selfid);
-}
-
-#elif !defined(__BIONIC__)
-
-// glibc doesn't implement or export either gettid or tgkill.
+// glibc doesn't implement or export tgkill.
 #include <unistd.h>
 #include <sys/syscall.h>
 
-pid_t gettid() {
-  return syscall(__NR_gettid);
-}
-
 int tgkill(int tgid, int tid, int sig) {
   return syscall(__NR_tgkill, tgid, tid, sig);
 }

libbacktrace/thread_utils.h

@@ -23,8 +23,6 @@ __BEGIN_DECLS
 
 int tgkill(int tgid, int tid, int sig);
 
-pid_t gettid();
-
 __END_DECLS
 
 #endif /* _LIBBACKTRACE_THREAD_UTILS_H */

libcutils/threads.c

@@ -35,12 +35,7 @@
 #ifndef __ANDROID__
 pid_t gettid() {
 #if defined(__APPLE__)
-  uint64_t owner;
-  int rc = pthread_threadid_np(NULL, &owner);
-  if (rc != 0) {
-    abort();
-  }
-  return owner;
+  return syscall(SYS_thread_selfid);
 #elif defined(__linux__)
   return syscall(__NR_gettid);
 #elif defined(_WIN32)