top-level/release.nix: add patchShebangs test

This is currently failing but nobody noticed!

pkgs/test/default.nix

@@ -27,4 +27,6 @@ with pkgs;
   macOSSierraShared = callPackage ./macos-sierra-shared {};
 
   cross = callPackage ./cross {};
+
+  patch-shebangs = callPackage ./patch-shebangs {};
 }

pkgs/test/patch-shebangs/default.nix

@@ -0,0 +1,26 @@
+{ stdenv, runCommand }:
+
+let
+  bad-shebang = stdenv.mkDerivation {
+    name         = "bad-shebang";
+    unpackPhase  = ":";
+    installPhase = ''
+      mkdir -p $out/bin
+      echo "#!/bin/sh" > $out/bin/test
+      echo "echo -n hello" >> $out/bin/test
+      chmod +x $out/bin/test
+    '';
+  };
+in runCommand "patch-shebangs-test" {
+  passthru = { inherit bad-shebang; };
+  meta.platforms = stdenv.lib.platforms.all;
+} ''
+  printf "checking whether patchShebangs works properly... ">&2
+  if ! grep -q '^#!/bin/sh' ${bad-shebang}/bin/test; then
+    echo "yes" >&2
+    touch $out
+  else
+    echo "no" >&2
+    exit 1
+  fi
+''

pkgs/top-level/release.nix

@@ -77,6 +77,7 @@ let
               jobs.tests.cc-wrapper-libcxx-39.x86_64-darwin
               jobs.tests.stdenv-inputs.x86_64-darwin
               jobs.tests.macOSSierraShared.x86_64-darwin
+              jobs.tests.patch-shebangs.x86_64-darwin
             ];
         } else null;
 
@@ -119,6 +120,7 @@ let
               jobs.tests.cc-multilib-gcc.x86_64-linux
               jobs.tests.cc-multilib-clang.x86_64-linux
               jobs.tests.stdenv-inputs.x86_64-linux
+              jobs.tests.patch-shebangs.x86_64-linux
             ]
             ++ lib.collect lib.isDerivation jobs.stdenvBootstrapTools
             ++ lib.optionals supportDarwin [
@@ -148,6 +150,7 @@ let
               jobs.tests.cc-wrapper-libcxx-6.x86_64-darwin
               jobs.tests.stdenv-inputs.x86_64-darwin
               jobs.tests.macOSSierraShared.x86_64-darwin
+              jobs.tests.patch-shebangs.x86_64-darwin
             ];
         };