fReopenDebugLog and fRequestShutdown should be type sig_atomic_t

This allows access as an atomic variable in the presence
of async interrupts.

See issue #7433 for more details
fixes: #7433

src/init.cpp

@@ -111,7 +111,7 @@ CClientUIInterface uiInterface; // Declared but not defined in ui_interface.h
 // shutdown thing.
 //
 
-volatile bool fRequestShutdown = false;
+volatile sig_atomic_t fRequestShutdown = false;
 
 void StartShutdown()
 {