[libFuzzer] AlrmHandler is executed in a different thread for Windows.

Don't check for InFuzzingThread() on Windows, since the AlarmHandler() is
always executed by a different thread from a thread pool.
If we don't add these changes, the alarm handler will never execute.
Note that we decided to ignore possible problem in the synchronization.

Differential Revision: https://reviews.llvm.org/D28723

llvm-svn: 292746

llvm/lib/Fuzzer/FuzzerLoop.cpp

@@ -296,7 +296,10 @@ void Fuzzer::InterruptCallback() {
 NO_SANITIZE_MEMORY
 void Fuzzer::AlarmCallback() {
   assert(Options.UnitTimeoutSec > 0);
+  // In Windows Alarm callback is executed by a different thread.
+#if !LIBFUZZER_WINDOWS
   if (!InFuzzingThread()) return;
+#endif
   if (!RunningCB)
     return; // We have not started running units yet.
   size_t Seconds =