rhash: fix build on darwin

Clang requires upstream patch to fix configure script

We're in crunch time for the 21.11 release and this causes lots of rebuilds,
so the patch is applied conditionally to give Hydra a break. After it
gets auto-merged into staging, I'll do a followup PR to make it
unconditional.

pkgs/tools/security/rhash/default.nix

@@ -1,6 +1,7 @@
 { lib
 , stdenv
 , fetchFromGitHub
+, fetchpatch
 , which
 , enableStatic ? stdenv.hostPlatform.isStatic
 }:
@@ -16,6 +17,14 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-HkDgWwHoRWCNtWyfP4sj3veEd+KT5J7yL4J4Z/hJcrE=";
   };
 
+  patches = lib.optionals stdenv.cc.isClang [
+    # Fix clang configuration; remove with next release
+    (fetchpatch {
+      url = "https://github.com/rhash/RHash/commit/4dc506066cf1727b021e6352535a8bb315c3f8dc.patch";
+      sha256 = "0i5jz2s37h278c8d36pzphhp8rjy660zmhpg2cqlp960f6ny8wwj";
+    })
+  ];
+
   nativeBuildInputs = [ which ];
 
   # configure script is not autotools-based, doesn't support these options