Always patch the interpreter of rustlib binaries

When using `stable.toolchain`,
`lib/rustlib/x86_64-unknown-linux-gnu/bin/rust-lld` and other binaries
in the same directory are not patched, so they do not work. I'm not sure
exactly when Rust uses these, but it seems to break cross-compilation to
`wasm32-unknown-unknown`.

Fix it by generalizing the patching applied to the `rustc` component.
Replace the glob with a `find` invocation to avoid errors on components
that have a `lib` directory but no `lib/rustlib/*/bin`.

lib/mk-toolchain.nix

@@ -42,29 +42,27 @@ let
                   patchelf --set-rpath ${rpath} "$file" || true
                 fi
               done
-            fi
 
-            if [ -d $out/libexec ]; then
-              for file in $(find $out/libexec -type f); do
+              for file in $(find $out/lib -path '*/bin/*' -type f); do
                 if isELF "$file"; then
                   patchelf \
                     --set-interpreter ${stdenv.cc.bintools.dynamicLinker} \
-                    --set-rpath ${rpath} \
+                    --set-rpath ${stdenv.cc.cc.lib}/lib:${rpath} \
                     "$file" || true
                 fi
               done
             fi
 
-            ${optionalString (component == "rustc") ''
-              for file in $(find $out/lib/rustlib/*/bin -type f); do
+            if [ -d $out/libexec ]; then
+              for file in $(find $out/libexec -type f); do
                 if isELF "$file"; then
                   patchelf \
                     --set-interpreter ${stdenv.cc.bintools.dynamicLinker} \
-                    --set-rpath ${stdenv.cc.cc.lib}/lib:${rpath} \
+                    --set-rpath ${rpath} \
                     "$file" || true
                 fi
               done
-            ''}
+            fi
 
             ${optionalString (component == "llvm-tools-preview") ''
               for file in $out/lib/rustlib/*/bin/*; do