gnu: Add rust-bencher.

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

gnu/packages/crates-io.scm

@@ -49,6 +49,28 @@ support.")
     (license (list license:asl2.0
                    license:expat))))
 
+(define-public rust-bencher
+  (package
+    (name "rust-bencher")
+    (version "0.1.5")
+    (source
+      (origin
+        (method url-fetch)
+        (uri (crate-uri "bencher" version))
+        (file-name (string-append name "-" version ".tar.gz"))
+        (sha256
+         (base32
+          "1x8p2xblgqssay8cdykp5pkfc0np0jk5bs5cx4f5av097aav9zbx"))))
+    (build-system cargo-build-system)
+    (home-page "https://github.com/bluss/bencher/")
+    (synopsis "Port of the libtest benchmark runner to Rust stable")
+    (description "This package provides a port of the libtest (unstable Rust)
+benchmark runner to Rust stable releases.  Supports running benchmarks and
+filtering based on the name.  Benchmark execution works exactly the same way
+and no more (caveat: black_box is still missing!).")
+    (license (list license:asl2.0
+                   license:expat))))
+
 (define-public rust-proc-macro2
   (package
     (name "rust-proc-macro2")