SYSENTER/SYSCALL support

. add cpufeature detection of both
	. use it for both ipc and kernelcall traps, using a register
	  for call number
	. SYSENTER/SYSCALL does not save any context, therefore userland
	  has to save it
	. to accomodate multiple kernel entry/exit types, the entry
	  type is recorded in the process struct. hitherto all types
	  were interrupt (soft int, exception, hard int); now SYSENTER/SYSCALL
	  is new, with the difference that context is not fully restored
	  from proc struct when running the process again. this can't be
	  done as some information is missing.
	. complication: cases in which the kernel has to fully change
	  process context (i.e. sigreturn). in that case the exit type
	  is changed from SYSENTER/SYSEXIT to soft-int (i.e. iret) and
	  context is fully restored from the proc struct. this does mean
	  the PC and SP must change, as the sysenter/sysexit userland code
	  will otherwise try to restore its own context. this is true in the
	  sigreturn case.
	. override all usage by setting libc_ipc=1

kernel/proc.h

@@ -159,6 +159,7 @@ struct proc {
 				   pick a new one. Process was dequeued and
 				   should be enqueued at the end of some run
 				   queue again */
+#define RTS_BOOTINHIBIT	0x10000	/* not ready until VM has made it */
 
 /* A process is runnable iff p_rts_flags == 0. */
 #define rts_f_is_runnable(flg)	((flg) == 0)