Use GNU tar format by default.

The default PAX format has issues with long file paths. If the complete path to
a file, including the package_dir prefix, exceeds 100 characters, Python will
incorrectly truncate it so the resulting path within the tar file does not have
the package_dir prefix. For example:
  File: path/to/file.txt
  Package dir: my_dir
  Expected path: my_dir/path/to/file.txt
  Resulting path: path/to/file.txt (if expected path > 100 chars)

Author: adamshapiro0

pkg/private/tar/tar.bzl

@@ -247,7 +247,7 @@ pkg_tar_impl = rule(
             doc = """Obsolete. Do not use.""",
             allow_files = True,
         ),
-        "format": attr.string(default = "DEFAULT"),
+        "format": attr.string(default = "GNU"),
         "mode": attr.string(),
         "modes": attr.string_dict(),
         "mtime": attr.int(default = _DEFAULT_MTIME),