[libFuzzer] Remove InterruptHandler from Fuchsia implementation

[eep]

Summary

As implemented, the InterruptHandler thread was spinning trying to
select() on a null "stdin", wasting a significant amount of CPU for no
benefit. As Fuchsia does not have a native concept of stdin (or POSIX
signals), this commit simply removes this feature entirely.

compiler-rt/lib/fuzzer/FuzzerUtilFuchsia.cpp

 
 void AlarmHandler(int Seconds) {
   while (true) {
     SleepSeconds(Seconds);
     Fuzzer::StaticAlarmCallback();
   }
 }
 
-void InterruptHandler() {
-  fd_set readfds;
-  // Ctrl-C sends ETX in Zircon.
-  do {
-    FD_ZERO(&readfds);
-    FD_SET(STDIN_FILENO, &readfds);
-    select(STDIN_FILENO + 1, &readfds, nullptr, nullptr, nullptr);
-  } while(!FD_ISSET(STDIN_FILENO, &readfds) || getchar() != 0x03);
-  Fuzzer::StaticInterruptCallback();
-}
-
 // CFAOffset is used to reference the stack pointer before entering the
 // trampoline (Stack Pointer + CFAOffset = prev Stack Pointer). Before jumping
 // to the trampoline we copy all the registers onto the stack. We need to make
 // sure that the new stack has enough space to store all the registers.
 //
 // The trampoline holds CFI information regarding the registers stored in the
 // stack, which is then used by the unwinder to restore them.
 #if defined(__x86_64__)
void SetSignalHandler(const FuzzingOptions &Options) {
   Printf("%s", Buf);
 
   // Set up alarm handler if needed.
   if (Options.HandleAlrm && Options.UnitTimeoutSec > 0) {
     std::thread T(AlarmHandler, Options.UnitTimeoutSec / 2 + 1);
     T.detach();
   }
 
-  // Set up interrupt handler if needed.
-  if (Options.HandleInt || Options.HandleTerm) {
-    std::thread T(InterruptHandler);
-    T.detach();
-  }
+  // Options.HandleInt and Options.HandleTerm are not supported on Fuchsia
 
   // Early exit if no crash handler needed.
   if (!Options.HandleSegv && !Options.HandleBus && !Options.HandleIll &&
       !Options.HandleFpe && !Options.HandleAbrt)
     return;
 
   // Set up the crash handler and wait until it is ready before proceeding.
   zx_handle_t Event;