Re: cargo-build-system: cargo-build-flags: --cfg=unix in package recipe

[Danny Milosavljevic]

It was missing in guix/build-system/cargo.scm cargo-build as a keyword 
parameter.

Adding

 (define* (cargo-build store name inputs
                       #:key
                       (tests? #t)
                       (test-target #f)
-                      (configure-flags #f)
+                      (configure-flags #f) ; XXX unused
+                      (cargo-build-flags ''("--release"))
                       (phases '(@ (guix build cargo-build-system)
                                   %standard-phases))
                       (outputs '("out"))
@@ -89,6 +99,7 @@ to NAME and VERSION."
                                  source))
                     #:system ,system
                     #:test-target ,test-target
+                    #:cargo-build-flags ,cargo-build-flags
                     #:tests? ,tests?

makes it work.