[panic.serial] Add location to panic data

Updated kassert to be an actual function, and used the __builtin_*
functions for location data. Updated the panic handler protocol to
include sending location data as three more parameters. Updated the
serial panic handler to display that data along with the (optional)
message.

src/kernel/panic.serial/entry.s

@@ -10,7 +10,7 @@ _panic_entry:
 	push 0 ; NMI doesn't push an error code
 	push 2 ; NMI is int 2
 	push_all
-	mov rdx, rsp
+	mov r9, rsp
 
 	mov rax, [rsp + REGS.rip]
 	push rax