emacs-build-system: Reinstate the check phase.

* guix/build/emacs-build-system.scm (%standard-phases): Reinstate the check
phase from the gnu-build-system.
* guix/build-system/emacs.scm (emacs-build)[tests?]: But do not enable it by default.
[parallel-tests?]: Add argument.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

guix/build-system/emacs.scm

@@ -82,7 +82,8 @@
 
 (define* (emacs-build store name inputs
                       #:key source
-                      (tests? #t)
+                      (tests? #f)
+                      (parallel-tests? #t)
                       (test-target "test")
                       (configure-flags ''())
                       (phases '(@ (guix build emacs-build-system)

guix/build/emacs-build-system.scm

@@ -246,7 +246,6 @@ second hyphen.  This corresponds to 'name-version' as used in ELPA packages."
     (add-after 'set-paths 'set-emacs-load-path set-emacs-load-path)
     (replace 'unpack unpack)
     (delete 'configure)
-    (delete 'check)
     ;; Move the build phase after install: the .el files are byte compiled
     ;; directly in the store.
     (delete 'build)