gnu: Add rust-webpki-0.18.

* gnu/packages/crates-io.scm (rust-webpki-0.18): New variable.

gnu/packages/crates-io.scm

@@ -26668,6 +26668,25 @@ protocol extensions.  Look at the crate wayland-client for usable bindings.")
 Verification.")
     (license license:isc)))
 
+(define-public rust-webpki-0.18
+  (package/inherit rust-webpki-0.21
+    (name "rust-webpki")
+    (version "0.18.1")
+    (source
+     (origin
+       (method url-fetch)
+       (uri (crate-uri "webpki" version))
+       (file-name (string-append name "-" version ".tar.gz"))
+       (sha256
+        (base32 "0zx1v8afa4ig97dyqfrnlj5i7pib6dnfw88qn2iiqhfq2rrrdmqp"))))
+    (build-system cargo-build-system)
+    (arguments
+     `(#:cargo-inputs
+       (("rust-ring" ,rust-ring-0.13)
+        ("rust-untrusted" ,rust-untrusted-0.6))
+       #:cargo-development-inputs
+       (("rust-base64" ,rust-base64-0.9))))))
+
 (define-public rust-weedle-0.10
   (package
     (name "rust-weedle")