tsan: remove thread initialization check from interceptors

[dvyukov]

Summary

Currently entry into each interceptor checks if the current thread
is initialized or not. This check seems to be unnecessary at least
on Linux. Remove the check.

[melver]

compiler-rt/lib/tsan/rtl/tsan_interceptors.h

44

Is this what breaks on other platforms?

[melver]

compiler-rt/lib/tsan/rtl/tsan_interceptors.h

44

Ah, what happens if !SANITIZER_CAN_USE_PREINIT_ARRAY?

compiler-rt/lib/tsan/rtl/tsan_interceptors.h

 LibIgnore *libignore();
 
 #if !SANITIZER_GO
 inline bool in_symbolizer() {
   return UNLIKELY(cur_thread_init()->in_symbolizer);
 }
 #endif
 
+ALWAYS_INLINE
+ThreadState *cur_thread_init_maybe() {
+#if SANITIZER_LINUX && !SANITIZER_ANDROID && defined(__x86_64__)
+  // On Linux we always have cur_thread initialized
+  // when we reach any interceptor. The main thread
+  // is initialized from .preinit_array, and other
+  // threads are initialized from _setjmp interceptor
+  // called from within pthread guts.
+  DCHECK(cur_thread());
+  return cur_thread();
+#else
+  return cur_thread_init();
+#endif
+}
+
 }  // namespace __tsan
 
 #define SCOPED_INTERCEPTOR_RAW(func, ...)      \
-  ThreadState *thr = cur_thread_init();        \
+  ThreadState *thr = cur_thread_init_maybe();  \
   const uptr caller_pc = GET_CALLER_PC();      \
   ScopedInterceptor si(thr, #func, caller_pc); \
   const uptr pc = GET_CURRENT_PC();            \
   (void)pc;
 
 #define SCOPED_TSAN_INTERCEPTOR(func, ...)                                \
   SCOPED_INTERCEPTOR_RAW(func, __VA_ARGS__);                              \
   if (REAL(func) == 0) {                                                  \