Don't use sig_atomic_t on Windows.

We don't setup signal handler on Windows, so we can replace
`volatil sig_atomic_t` by simple `bool`.

src/server/kiwix-serve.cpp

@@ -111,10 +111,9 @@ inline std::string normalizeRootUrl(std::string rootUrl)
   return rootUrl.empty() ? rootUrl : "/" + rootUrl;
 }
 
+#ifndef _WIN32
 volatile sig_atomic_t waiting = false;
 volatile sig_atomic_t libraryMustBeReloaded = false;
-
-#ifndef _WIN32
 void handle_sigterm(int signum)
 {
     if ( waiting == false ) {
@@ -144,6 +143,9 @@ void setup_sighandlers()
     set_signal_handler(SIGINT,  &handle_sigterm);
     set_signal_handler(SIGHUP,  &handle_sighup);
 }
+#else
+bool waiting = false;
+bool libraryMustBeReloaded = false;
 #endif
 
 uint64_t fileModificationTime(const std::string& path)