daemon: Emit a 'build-succeeded' event in check mode.

Until now, something like "guix build sed -v1 --check" would not get a
'build-succeeded' event, which in turn meant that the spinner would not
be erased upon build completion.

* nix/libstore/build.cc (DerivationGoal::registerOutputs): When
'buildMode' is bmCheck and 'settings.printBuildTrace' emit a
"@ build-succeeded" trace upon success.
* tests/store.scm ("build-succeeded trace in check mode"): New test.

tests/store.scm

@@ -917,6 +917,19 @@
                                 (build-mode check))
                   #f))))))))
 
+(test-assert "build-succeeded trace in check mode"
+  (string-contains
+   (call-with-output-string
+     (lambda (port)
+       (let ((d (build-expression->derivation
+                 %store "foo" '(mkdir (assoc-ref %outputs "out"))
+                 #:guile-for-build
+                 (package-derivation %store %bootstrap-guile))))
+         (build-derivations %store (list d))
+         (parameterize ((current-build-output-port port))
+           (build-derivations %store (list d) (build-mode check))))))
+   "@ build-succeeded"))
+
 (test-assert "build multiple times"
   (with-store store
     ;; Ask to build twice.