array: make .set() private + format

compiler/main.v

@@ -311,7 +311,7 @@ fn (v mut V) compile() {
 		d.writeln(v.prof_counters())
 	}
 	dd := d.str()
-	cgen.lines.set(defs_pos, dd)// TODO `def.str()` doesn't compile
+	cgen.lines[defs_pos] = dd// TODO `def.str()` doesn't compile
 
   v.generate_main()
 

vlib/builtin/array.v

@@ -153,7 +153,7 @@ pub fn (s array) slice(start, _end int) array {
 	return res
 }
 
-pub fn (a mut array) set(idx int, val voidptr) {
+fn (a mut array) set(idx int, val voidptr) {
 	if idx < 0 || idx >= a.len {
 		panic('array index out of range: $idx / $a.len')
 	}