[libc/libos] code seperation

[Meulengracht]

We are currently in the progress of splitting up most of the service/syscall-api code into libos, and then keep libc clean in the sense that it should only interact with code from libos, instead of acting directly with system calls and system services.

This means we would like to end the most of the interactions that libc has with gracht+system calls.

Things that remain:

• All file related functions currently invoke the system service protocol directly.
• All socket related functions currently invoke the system service protocol directly.
• events.h needs a corresponding implementation in libos with type header and normal header
• signal.c uses both system call and process service directly
• exit.c uses the thread system call directly