crc32c: fix tests on darwin

Fix test library loading by enabling build-time rpath

pkgs/development/libraries/crc32c/default.nix

···
     "-DCRC32C_BUILD_BENCHMARKS=0"
     "-DCRC32C_USE_GLOG=0"
     "-DBUILD_SHARED_LIBS=${if staticOnly then "0" else "1"}"
+  ] ++ lib.optionals stdenv.isDarwin [
+    "-DCMAKE_SKIP_BUILD_RPATH=OFF" # for tests
   ];
 
   doCheck = false;