gnu: guile-ncurses: Build a UTF-8 locale for the tests.

* gnu/packages/guile.scm (guile-ncurses)[arguments]: Add 'install-locales'
  phase.

gnu/packages/guile.scm

@@ -262,7 +262,16 @@ (define-public guile-ncurses
                       (("\"libguile-ncurses\"")
                        (format #f "\"~a/lib/libguile-ncurses\""
                                out)))))
-                 %standard-phases)))
+                 (alist-cons-before
+                  'check 'install-locales
+                  (lambda _
+                    ;; One of the tests requires the availability of a UTF-8
+                    ;; locale and otherwise fails.
+                    (setenv "LOCPATH" (getcwd))
+                    (zero? (system* "localedef" "--no-archive"
+                                    "--prefix" (getcwd) "-i" "en_US"
+                                    "-f" "UTF-8" "./en_US.utf8")))
+                  %standard-phases))))
     (home-page "http://www.gnu.org/software/guile-ncurses/")
     (synopsis "Guile bindings to ncurses")
     (description