buildBazelPackage: prime fixed output derivations

All bazel fixed output derivations should be specific to the bazel
version that was used to generate them. There is not guarantee that the
build will still succeed or reproduces (without the cached fixed output)
if the fetch phase wasn't rerun with a different bazel version.

In the past bazel had been bumped but not all those packages that have
fixed outputs from bazel builds. This lead to compiling and somewhat
working TF versions that couldn't be reproduced without the cached fixed
outputs.

pkgs/build-support/build-bazel-package/default.nix

@@ -122,6 +122,8 @@ in stdenv.mkDerivation (fBuildAttrs // {
 
       cp -r $bazelOut/external $out
 
+      echo '${bazel.name}' > $out/.nix-bazel-version
+
       runHook postInstall
     '';
 
@@ -143,6 +145,14 @@ in stdenv.mkDerivation (fBuildAttrs // {
 
   preConfigure = ''
     mkdir -p "$bazelOut"
+
+    test "${bazel.name}" = "$(<$deps/.nix-bazel-version)" || {
+      echo "fixed output derivation was built for a different bazel version" >&2
+      echo "     got: $(<$deps/.nix-bazel-version)" >&2
+      echo "expected: ${bazel.name}" >&2
+      exit 1
+    }
+
     cp -r $deps $bazelOut/external
     chmod -R +w $bazelOut
     find $bazelOut -type l | while read symlink; do