gnu: Add rust-cfg-if-0.1.

* gnu/packages/rust-cbindgen.scm (rust-cfg-if-0.1): New hidden variable.

gnu/packages/rust-cbindgen.scm

@@ -106,3 +106,25 @@ (define rust-bitflags-1.1
     (properties '((hidden? . #t)))
     (license (list license:asl2.0
                    license:expat))))
+
+(define rust-cfg-if-0.1
+  (package
+    (name "rust-cfg-if")
+    (version "0.1.10")
+    (source
+      (origin
+        (method url-fetch)
+        (uri (crate-uri "cfg-if" version))
+        (file-name (string-append name "-" version ".crate"))
+        (sha256
+         (base32
+          "08h80ihs74jcyp24cd75wwabygbbdgl05k6p5dmq8akbr78vv1a7"))))
+    (build-system cargo-build-system)
+    (home-page "https://github.com/alexcrichton/cfg-if")
+    (synopsis "Define an item depending on parameters")
+    (description "This package provides a macro to ergonomically define an item
+depending on a large number of #[cfg] parameters.  Structured like an
+@code{if-else} chain, the first matching branch is the item that gets emitted.")
+    (properties '((hidden? . #t)))
+    (license (list license:asl2.0
+                   license:expat))))