This removes the `__sanitizer_*` allocation function definitions from
`hwasan_interceptors.cpp` and moves them into their own file. This way
implementations that do not use interceptors at all can just ignore
(almost) everything in `hwasan_interceptors.cpp`.
Also remove some unused headers in `hwasan_interceptors.cpp` after the move.
Differential Revision: https://reviews.llvm.org/D103564