Get rid of gcc, adds exit()

core.asm

@@ -1,3 +1,4 @@
+extern	NR_exit
 extern	strclr
 
 section	.text
@@ -10,6 +11,7 @@ section	.text
 	global	tolower
 	global	toupper
 	global	itoa
+	global	exit
 
 ;----- min(int a, int b) -----;
 ; return value: lowest value
@@ -176,3 +178,8 @@ itoa:
 	pop	rax
 	leave
 	ret
+;----- exit(int exit_code) -----;
+; returns: nothing
+exit:
+	mov	rax, NR_exit
+	syscall