AT_ERROR if mmap allocation has failed (#46934)
Summary:
All other system call failures in `THMapAllocator` constructor are considered failures, but this one, for some reason was not
Fixes https://github.com/pytorch/pytorch/issues/46651
Pull Request resolved: https://github.com/pytorch/pytorch/pull/46934
Reviewed By: walterddr, seemethere
Differential Revision: D24572657
Pulled By: malfet
fbshipit-source-id: 0a2b6ce78d5484190536bc4949fc4697d6387ab8
