Rename wsutil/process.h to wsutil/processes.h to avoid collisions.

Rename wsutil/process.h to wsutil/processes.h to avoid collisions.

The MSVC rules for searching for headers are a huge barrel of fun; it
appears that, for some files that need the MSVC <process.h> to declare
getpid(), they're getting our <wsutil/process.h> instead, as that's in
the current directory.  Rename it to avoid the collision.

Change-Id: I88eb70237062fa7957e38d7ff8132524390a6a5c
Reviewed-on: https://code.wireshark.org/review/8870
Reviewed-by: Guy Harris <guy@alum.mit.edu>