Make some more threads receive interrupts

Shouldn't hurt to do this. In particular, this should speed up
shutting down the PathSubstitutionGoal thread if it's copying from a
remote store.

src/libstore/build/substitution-goal.cc

@@ -2,6 +2,7 @@
 #include "substitution-goal.hh"
 #include "nar-info.hh"
 #include "finally.hh"
+#include "signals.hh"
 
 namespace nix {
 
@@ -217,6 +218,8 @@ void PathSubstitutionGoal::tryToRun()
 
     thr = std::thread([this]() {
         try {
+            ReceiveInterrupts receiveInterrupts;
+
             /* Wake up the worker loop when we're done. */
             Finally updateStats([this]() { outPipe.writeSide.close(); });
 

src/libutil/thread-pool.cc

@@ -79,6 +79,8 @@ void ThreadPool::process()
 
 void ThreadPool::doWork(bool mainThread)
 {
+    ReceiveInterrupts receiveInterrupts;
+
     if (!mainThread)
         interruptCheck = [&]() { return (bool) quit; };