Just split the comment for struct's one and array's one.

(gdb) ptype/o struct RString
/* offset    |  size */  type = struct RString {
/*    0      |    16 */    struct RBasic {
/*    0      |     8 */        VALUE flags;
/*    8      |     8 */        const VALUE klass;

                               /* total size (bytes):   16 */
                           } basic;
/*   16      |    24 */    union {
/*                24 */        struct {
/*   16      |     8 */            long len;
/*   24      |     8 */            char *ptr;
/*   32      |     8 */            union {
/*                 8 */                long capa;
/*                 8 */                VALUE shared;

                                       /* total size (bytes):    8 */
                                   } aux;

                                   /* total size (bytes):   24 */
                               } heap;
/*                24 */        struct {
/*   16      |    24 */            char ary[24];

                                   /* total size (bytes):   24 */
                               } embed;
/* XXX  8-byte padding  */

                               /* total size (bytes):   24 */
                           } as;

                           /* total size (bytes):   40 */
                         }
(gdb)

This commit adds support for embedded strings with variable capacity and
uses Variable Width Allocation to allocate strings.

Linking printf family functions makes mjit objects to link
unnecessary code.

Must not be a bad idea to improve documents. [ci skip]

Must not be a bad idea to improve documents. [ci skip]

Must not be a bad idea to improve documents. [ci skip]

Must not be a bad idea to improve documents. [ci skip]

Must not be a bad idea to improve documents. [ci skip]