Kernel: Add basic concept of Processes

We now create Shell as a process that has its own threads

libc/include/sys/types.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <stdint.h>
+#include <sys/cdefs.h>
+
+__BEGIN_DECLS
+
+typedef int32_t pid_t;
+
+__END_DECLS