Fix namedtensor build (#21609)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/21609
ghimport-source-id: 648a0bcd28db2cdda1bf2fa6a904ca8f851088c2
Differential Revision: D15747687
Pulled By: zou3519
fbshipit-source-id: 2a972a15fa7399391617fc6e6b19879b86568c3a
