[tsan] Move emptyset/oldset to ThreadSignalContext.

[yabinc]

Summary

Android doesn't support __thread keyword. So move emptyset/oldset
from THREADLOCAL to ThreadSignalContext.

lib/tsan/rtl/tsan_interceptors.cc

struct SignalDesc {
   ucontext_t ctx;
 };
 
 struct ThreadSignalContext {
   int int_signal_send;
   atomic_uintptr_t in_blocking_func;
   atomic_uintptr_t have_pending_signals;
   SignalDesc pending_signals[kSigCount];
+  // emptyset and oldset are too big for stack.
+  __sanitizer_sigset_t emptyset;
+  __sanitizer_sigset_t oldset;
 };
 
 // The object is 64-byte aligned, because we want hot data to be located in
 // a single cache line if possible (it's accessed in every interceptor).
 static ALIGNED(64) char libignore_placeholder[sizeof(LibIgnore)];
 static LibIgnore *libignore() {
   return reinterpret_cast<LibIgnore*>(&libignore_placeholder[0]);
 }

 
 void ProcessPendingSignals(ThreadState *thr) {
   ThreadSignalContext *sctx = SigCtx(thr);
   if (sctx == 0 ||
       atomic_load(&sctx->have_pending_signals, memory_order_relaxed) == 0)
     return;
   atomic_store(&sctx->have_pending_signals, 0, memory_order_relaxed);
   atomic_fetch_add(&thr->in_signal_handler, 1, memory_order_relaxed);
-  // These are too big for stack.
-  static THREADLOCAL __sanitizer_sigset_t emptyset, oldset;
-  CHECK_EQ(0, REAL(sigfillset)(&emptyset));
-  CHECK_EQ(0, pthread_sigmask(SIG_SETMASK, &emptyset, &oldset));
+  CHECK_EQ(0, REAL(sigfillset)(&sctx->emptyset));
+  CHECK_EQ(0, pthread_sigmask(SIG_SETMASK, &sctx->emptyset, &sctx->oldset));
   for (int sig = 0; sig < kSigCount; sig++) {
     SignalDesc *signal = &sctx->pending_signals[sig];
     if (signal->armed) {
       signal->armed = false;
       CallUserSignalHandler(thr, false, true, signal->sigaction, sig,
           &signal->siginfo, &signal->ctx);
     }
   }
-  CHECK_EQ(0, pthread_sigmask(SIG_SETMASK, &oldset, 0));
+  CHECK_EQ(0, pthread_sigmask(SIG_SETMASK, &sctx->oldset, 0));
   atomic_fetch_add(&thr->in_signal_handler, -1, memory_order_relaxed);
 }
 
 }  // namespace __tsan
 
 static bool is_sync_signal(ThreadSignalContext *sctx, int sig) {
   return sig == SIGSEGV || sig == SIGBUS || sig == SIGILL ||
       sig == SIGABRT || sig == SIGFPE || sig == SIGPIPE || sig == SIGSYS ||