Add support for include-what-you-use (#71114)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/71114
`include-what-you-use` or `iwyu` is a clang-based tool that looks at
the code's AST to figure out which symbols need to be included and
with the help of user-defined mappings it suggests the include
files that are actually needed.
This is very nice for the per-operator headers build because it give
you a list of exactly the `ATen/ops` headers needed by the file. You
still need to manually write the include-guards etc. but at least this
automates the most tedious part.
The header mappings aren't perfect yet so it will still suggest you
include basic c10 components everywhere instead of taking it
transitively from `TensorBase.h`. However, this does provide some
useful mappings and removes bad include paths from the build system
that were causing bad suggestions.
Test Plan: Imported from OSS
Reviewed By: ngimel
Differential Revision: D33949901
Pulled By: malfet
fbshipit-source-id: d5b015ef9e168bee4b8717b8e87ccc0608da62a1
(cherry picked from commit ecb2ffb35a5b1509a1275834fbe5c25e60ea1b79)
