xxhash r42 (new formula)

Closes Homebrew/homebrew#44398.

Signed-off-by: Alex Dunn <dunn.alex@gmail.com>

Formula/xxhash.rb

@@ -0,0 +1,17 @@
+class Xxhash < Formula
+  desc "Extremely fast non-cryptographic hash algorithm"
+  homepage "https://github.com/Cyan4973/xxHash"
+  url "https://github.com/Cyan4973/xxHash/archive/r42.tar.gz"
+  version "r42"
+  sha256 "d21dba3ebf5ea8bf2f587150230189231c8d47e8b63c865c585b08d14c8218b8"
+
+  def install
+    system "make"
+    bin.install "xxhsum"
+  end
+
+  test do
+    (testpath/"leaflet.txt").write "No computer should be without one!"
+    assert_match /^67bc7cc242ebc50a/, shell_output("#{bin}/xxhsum leaflet.txt")
+  end
+end