build-system/gnu: Rename "make dist" phase to 'build-dist'.

* guix/build/gnu-dist.scm (%dist-phases): Add BUILD under the name
'build-dist'.

guix/build/gnu-dist.scm

@@ -54,6 +54,7 @@ (define %dist-phases
   (modify-phases %standard-phases
     (delete 'strip)
     (replace 'install install-dist)
-    (replace 'build build)))
+    (add-after 'build 'build-dist build)
+    (delete 'build)))
 
 ;;; gnu-dist.scm ends here