tsan: fix crash during thread exit

[dvyukov]

Summary

Use of gethostent provokes caching of some resources inside of libc.
They are freed in libc_thread_freeres very late in thread lifetime,
after our ThreadFinish. libc_thread_freeres calls free which
previously crashed in malloc hooks.
Fix it by setting ignore_interceptors for finished threads,
which in turn prevents malloc hooks.

compiler-rt/lib/tsan/rtl/tsan_rtl_thread.cpp

 void ThreadFinish(ThreadState *thr) {
   ThreadCheckIgnore(thr);
   if (thr->stk_addr && thr->stk_size)
     DontNeedShadowFor(thr->stk_addr, thr->stk_size);
   if (thr->tls_addr && thr->tls_size)
     DontNeedShadowFor(thr->tls_addr, thr->tls_size);
   thr->is_dead = true;
   thr->is_inited = false;
+#if !SANITIZER_GO
+  thr->ignore_interceptors++;
+#endif
   ctx->thread_registry.FinishThread(thr->tid);
 }
 
 void ThreadContext::OnFinished() {
   if (!detached) {
     thr->fast_state.IncrementEpoch();
     // Can't increment epoch w/o writing to the trace as well.
     TraceAddEvent(thr, thr->fast_state, EventTypeMop, 0);

compiler-rt/test/tsan/Linux/sethostent.cpp

+// RUN: %clang_tsan -O1 %s -o %t && %run %t 2>&1 | FileCheck %s
+
+// Use of gethostent provokes caching of some resources inside of libc.
+// They are freed in __libc_thread_freeres very late in thread lifetime,
+// after our ThreadFinish. __libc_thread_freeres calls free which
+// previously crashed in malloc hooks.
+
+#include "../test.h"
+#include <netdb.h>
+
+long X;
+
+extern "C" void __sanitizer_malloc_hook(void *ptr, size_t size) {
+  __atomic_fetch_add(&X, 1, __ATOMIC_RELAXED);
+}
+
+extern "C" void __sanitizer_free_hook(void *ptr) {
+  __atomic_fetch_sub(&X, 1, __ATOMIC_RELAXED);
+}
+
+void *Thread(void *x) {
+  sethostent(1);
+  gethostbyname("llvm.org");
+  gethostent();
+  endhostent();
+  return NULL;
+}
+
+int main() {
+  pthread_t th;
+  pthread_create(&th, NULL, Thread, NULL);
+  pthread_join(th, NULL);
+  fprintf(stderr, "DONE\n");
+  return 0;
+}
+
+// CHECK: DONE