Kernel/LibC: Add initial pseudo terminal support

This patch implements posix_openpt() and ptsname()

grantpt() and unlockpt() are left in LibC as stubs, as posix_openpt
currently does all of the needed work.

userspace/libraries/LibC/include/sys/syscall.h

@@ -88,6 +88,8 @@ __BEGIN_DECLS
 	O(SYS_SIGPENDING,		sigpending)		\
 	O(SYS_SIGPROCMASK,		sigprocmask)	\
 	O(SYS_SETITIMER,		setitimer)		\
+	O(SYS_POSIX_OPENPT,		posix_openpt)	\
+	O(SYS_PTSNAME,			ptsname)		\
 
 enum Syscall
 {