Fall back to TCP connect ping on Windows without pcap

While Windows raw sockets can send and receive ICMP packets, Nmap relies on
libpcap packet capture to spot responses, so if pcap isn't available
(--unprivileged or Npcap not installed), we need to fall back to TCP connect for
host discovery, just like we do for unprivileged users on other operating
systems. Previous behavior was a fatal error suggesting unhelpfully to use
--unprivileged.

Author: bonsaiviking

nmap.cc

@@ -479,7 +479,6 @@ void validate_scan_lists(scan_lists &ports, NmapOps &o) {
     o.pingtype |= PINGTYPE_TCP_USE_SYN;
   }
 
-#ifndef WIN32	/*	Win32 has perfectly fine ICMP socket support */
   if (!o.isr00t) {
     if (o.pingtype & (PINGTYPE_ICMP_PING | PINGTYPE_ICMP_MASK | PINGTYPE_ICMP_TS)) {
       error("Warning:  You are not root -- using TCP pingscan rather than ICMP");
@@ -490,7 +489,6 @@ void validate_scan_lists(scan_lists &ports, NmapOps &o) {
       }
     }
   }
-#endif
 }
 
 struct ftpinfo ftp = get_default_ftpinfo();