Rename stdin, etc. in Subprocess to work with MSVC

Rename stdin, etc. in Subprocess to work with MSVC

Summary:
`stdin`, `stdout` and `stderr` are macros that expand to function calls with the MSVC CRT implementation. This is also the case for musl-libc. This means that Subprocess simply cannot be compiled on those platforms without changing the API.
To solve that, we change the API and deprecate the old API.

For more fun, `stdin`, `stdout` and `stderr` are also macros in glibc, they just expand to other identifiers rather than a function call.

Reviewed By: yfeldblum

Differential Revision: D4229544

fbshipit-source-id: 97f1a3b228b83cfdcaffee56d729063ea235e608