static initialization order with mutex (#28243)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28243
When building static libs version of pytorch 1.3 on windows (msvc v141), program crashes with bad memory reference because `fusion_backends_lock_` has not been initialized yet.
Test Plan:
sandcastle green,
tested locally on MSVC static builds that this fixes initialization.
Differential Revision: D17985919
fbshipit-source-id: ebd6178dedf5147d01c2c1754a0942a1bbbc7e34
