gnu: xmagnify: Use cc-for-target.

* gnu/packages/accessibility.scm (xmagnify)[arguments]: Replace
hard-coded gcc with cc-for-target in make-flags.

gnu/packages/accessibility.scm

@@ -309,7 +309,7 @@ (define-public xmagnify
     (arguments
      `(#:tests? #f ; none included
        #:make-flags
-       (list "CC=gcc"
+       (list (string-append "CC=" ,(cc-for-target))
              (string-append "prefix=" (assoc-ref %outputs "out")))
        #:phases
        (modify-phases %standard-phases