cudnn_cudatookit_11: add $ORIGIN/ to library RPATHs

Starting with version 8, CuDNN consists of multiple libraries.
Libraries (except libcudnn.so) are dlopen()ed on demand.

Since the CuDNN library path itself was not added to the rpath of the
libraries, use of CuDNN often fails with the following error:

Could not load library libcudnn_cnn_train.so.8.
Error: libcudnn_ops_train.so.8: cannot open shared object file: No such file or directory
Please make sure libcudnn_cnn_train.so.8 is in your library path!

This change fixes this by adding $ORIGIN/ to the rpath of all CuDNN
libraries.

pkgs/development/libraries/science/math/cudnn/generic.nix

@@ -25,9 +25,12 @@ stdenv.mkDerivation {
   installPhase = ''
     function fixRunPath {
       p=$(patchelf --print-rpath $1)
-      patchelf --set-rpath "$p:${lib.makeLibraryPath [ stdenv.cc.cc ]}" $1
+      patchelf --set-rpath "''${p:+$p:}${lib.makeLibraryPath [ stdenv.cc.cc ]}:\$ORIGIN/" $1
     }
-    fixRunPath lib64/libcudnn.so
+
+    for lib in lib64/lib*.so; do
+      fixRunPath $lib
+    done
 
     mkdir -p $out
     cp -a include $out/include