gnu: Add rust-bitflags.

* gnu/packages/crates-io.scm (rust-bitflags): New variable.

gnu/packages/crates-io.scm

@@ -71,6 +71,26 @@ and no more (caveat: black_box is still missing!).")
     (license (list license:asl2.0
                    license:expat))))
 
+(define-public rust-bitflags
+  (package
+    (name "rust-bitflags")
+    (version "1.1.0")
+    (source
+      (origin
+        (method url-fetch)
+        (uri (crate-uri "bitflags" version))
+        (file-name (string-append name "-" version ".tar.gz"))
+        (sha256
+         (base32
+          "1zc1qb1hwsnl2d8rhzicsv9kqd5b2hwbrscrcfw5as4sfr35659x"))))
+    (build-system cargo-build-system)
+    (home-page "https://github.com/bitflags/bitflags")
+    (synopsis "Macro to generate structures which behave like bitflags")
+    (description "This package provides a macro to generate structures which
+behave like a set of bitflags.")
+    (license (list license:asl2.0
+                   license:expat))))
+
 (define-public rust-proc-macro2
   (package
     (name "rust-proc-macro2")