[compiler-rt] [sanitizer] Add cloak_sanitizer_signal_handlers runtime option (PR #162746)

[Vitaly Buka via llvm-commits]

================
@@ -24,6 +24,9 @@ namespace __sanitizer {
 
 const char *SanitizerToolName = "SanitizerTool";
 
+const int MaxSignals = 64;
+bool signal_handler_is_from_sanitizer[MaxSignals] = {0};
----------------
vitalybuka wrote:

> if (IsSignalHandlerFromSanitizer(signum) && ret == 0) {
>     if (act)
>       // If the user sets a signal handler, it is never cloaked, even if they
>       // reuse a sanitizer's signal handler.
>       SetSignalHandlerFromSanitizer(signum, false);
> 
>     ...
>   }

why do we need to check act?

```
  if (ret == 0 && SetSignalHandlerFromSanitizer(signum, false) ) {
        ...
  }
```

https://github.com/llvm/llvm-project/pull/162746