gnu: go-github.com-jtolds-gls: Skip tests with gccgo.

* gnu/packages/golang.scm (go-github.com-ktolds-gls)[arguments]: Don't
run the test suite when building with gccgo.

gnu/packages/golang.scm

@@ -2439,7 +2439,16 @@ (define-public go-github.com-jtolds-gls
                 "1k7xd2q2ysv2xsh373qs801v6f359240kx0vrl0ydh7731lngvk6"))))
     (build-system go-build-system)
     (arguments
-     '(#:import-path "github.com/jtolds/gls"))
+     (list
+       #:import-path "github.com/jtolds/gls"
+       #:phases
+       #~(modify-phases %standard-phases
+           (replace 'check
+             (lambda* (#:key inputs #:allow-other-keys #:rest args)
+               (unless
+                 ;; The tests fail when run with gccgo.
+                 (false-if-exception (search-input-file inputs "/bin/gccgo"))
+                 (apply (assoc-ref %standard-phases 'check) args)))))))
     (synopsis "@code{gls} provides Goroutine local storage")
     (description
      "The @code{gls} package provides a way to store a retrieve values