fix SIGINT handler in swift-frontend

motivation: fix regression where SIGINT would not terminate frontend processes

changes:
* call DispatchSourceSignal::resume
* call signal(SIGINT, SIG_IGN)

rdar://95862616

Author: tomerd

Sources/swift-driver/main.swift

@@ -45,14 +45,17 @@ func getExitCode(_ code: Int32) -> Int32 {
 }
 
 do {
-
+  #if !os(Windows)
+  signal(SIGINT, SIG_IGN)
+  #endif
   let processSet = ProcessSet()
   interruptSignalSource.setEventHandler {
     // Terminate running compiler jobs and let the driver exit gracefully, remembering
     // to return a corresponding exit code when done.
     processSet.terminate()
     driverInterrupted = true
   }
+  interruptSignalSource.resume()
 
   if ProcessEnv.vars["SWIFT_ENABLE_EXPLICIT_MODULE"] != nil {
     CommandLine.arguments.append("-explicit-module-build")