gnu: go-golang-org-x-time: Enable tests.

* gnu/packages/golang-build.scm (go-golang-org-x-time): Apply new
package style.
[arguments]: <#:phases>: Use custom 'check phase.

Change-Id: If6b9aa9198748c4b8a2fdc23cd723aec740eb533

gnu/packages/golang-build.scm

@@ -547,13 +547,18 @@ processing.")
         (base32 "1dahq0p6zn2pd408q6hsv1jl12nqrwd1gkl3r3dysk2q0z16192v"))))
     (build-system go-build-system)
     (arguments
-     `(#:import-path "golang.org/x/time"
-       ;; Source-only package
-       #:tests? #f
-       #:phases
-       (modify-phases %standard-phases
-         ;; Source-only package
-         (delete 'build))))
+     (list
+      #:import-path "golang.org/x/time"
+      #:phases
+      #~(modify-phases %standard-phases
+          ;; XXX: Workaround for go-build-system's lack of Go modules
+          ;; support.
+          (delete 'build)
+          (replace 'check
+            (lambda* (#:key tests? import-path #:allow-other-keys)
+              (when tests?
+                (with-directory-excursion (string-append "src/" import-path)
+                  (invoke "go" "test" "-v" "./..."))))))))
     (home-page "https://godoc.org/golang.org/x/time/rate")
     (synopsis "Supplemental Go time libraries")
     (description