builtin: define atoi & ftell

vlib/builtin/cfns.c.v

@@ -1,5 +1,7 @@
 module builtin
 
+// struct C.FILE {}
+
 // <string.h>
 fn C.memcpy(dest voidptr, const_src voidptr, n usize) voidptr
 
@@ -12,6 +14,8 @@ fn C.memset(str voidptr, c int, n usize) voidptr
 [trusted]
 fn C.calloc(int, int) &u8
 
+fn C.atoi(&char) int
+
 fn C.malloc(int) &u8
 
 fn C.realloc(a &u8, b int) &u8
@@ -120,6 +124,8 @@ fn C.chdir(path &char) int
 
 fn C.rewind(stream &C.FILE) int
 
+fn C.ftell(&C.FILE) int
+
 fn C.stat(&char, voidptr) int
 
 fn C.lstat(path &char, buf &C.stat) int