proper initialization of struct RVALUE

This changeset makes no difference unless GC_DEBUG is on.  When that flag is
set, struct RVALUE is bigger than struct RObject.  We have to take care of the
additional fields.  Otherwise we get a SIGSEGV like shown below.

The way obj is initialized in this patch works for both GC_DEBUG is on and off.
See also ISO/IEC 9899:1999 section 6.7.8 paragraph ruby#21.

```
Program received signal SIGSEGV, Segmentation fault.
__strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:62
62      ../sysdeps/x86_64/multiarch/strlen-avx2.S: No such file or directory
(gdb) bt
#0  __strlen_avx2 () at ../sysdeps/x86_64/multiarch/strlen-avx2.S:62
#1  0x00005555557dd9a7 in BSD_vfprintf (fp=0x7fffffff6be0, fmt0=0x5555558f3059 "@%s:%d", ap=0x7fffffff6dd0) at vsnprintf.c:1027
#2  0x00005555557db6f5 in ruby_do_vsnprintf (str=0x555555bfc58d <obj_info_buffers+1325> "", n=211, fmt=0x5555558f3059 "@%s:%d", ap=0x7fffffff6dd0) at sprintf.c:1022
#3  0x00005555557db909 in ruby_snprintf (str=0x555555bfc58d <obj_info_buffers+1325> "", n=211, fmt=0x5555558f3059 "@%s:%d") at sprintf.c:1040
#4  0x0000555555661ef4 in rb_raw_obj_info (buff=0x555555bfc560 <obj_info_buffers+1280> "0x0000555555d2bfa0 [0     ] T_STRING (String)", buff_size=256, obj=93825000456096) at gc.c:11449
#5  0x000055555565baaf in obj_info (obj=93825000456096) at gc.c:11612
#6  0x000055555565bae1 in rgengc_remembered (objspace=0x555555c0a1c0, obj=93825000456096) at gc.c:6618
#7  0x0000555555666987 in newobj_init (klass=93824999964192, flags=5, v1=0, v2=0, v3=0, wb_protected=1, objspace=0x555555c0a1c0, obj=93825000456096) at gc.c:2134
#8  0x0000555555666e49 in newobj_slowpath (klass=93824999964192, flags=5, v1=0, v2=0, v3=0, objspace=0x555555c0a1c0, wb_protected=1) at gc.c:2209
#9  0x0000555555666b94 in newobj_slowpath_wb_protected (klass=93824999964192, flags=5, v1=0, v2=0, v3=0, objspace=0x555555c0a1c0) at gc.c:2220
#10 0x000055555565751b in newobj_of (klass=93824999964192, flags=5, v1=0, v2=0, v3=0, wb_protected=1) at gc.c:2256
#11 0x00005555556575ca in rb_wb_protected_newobj_of (klass=93824999964192, flags=5) at gc.c:2272
#12 0x00005555557f36ea in str_alloc (klass=93824999964192) at string.c:728
#13 0x00005555557f2128 in rb_str_buf_new (capa=0) at string.c:1317
#14 0x000055555578c66d in rb_reg_preprocess (p=0x555555cc8148 "^-(.)(.+)?", end=0x555555cc8152 "", enc=0x555555cc7c80, fixed_enc=0x7fffffff74e8, err=0x7fffffff75f0 "") at re.c:2682
#15 0x000055555578ea13 in rb_reg_initialize (obj=93825000046736, s=0x555555cc8148 "^-(.)(.+)?", len=10, enc=0x555555cc7c80, options=0, err=0x7fffffff75f0 "", sourcefile=0x555555d1a5c0 "lib/optparse.rb", sourceline=1460) at re.c:2808
#16 0x000055555578e285 in rb_reg_initialize_str (obj=93825000046736, str=93825000046904, options=0, err=0x7fffffff75f0 "", sourcefile=0x555555d1a5c0 "lib/optparse.rb", sourceline=1460) at re.c:2869
ruby#17 0x000055555578ee02 in rb_reg_compile (str=93825000046904, options=0, sourcefile=0x555555d1a5c0 "lib/optparse.rb", sourceline=1460) at re.c:2958
ruby#18 0x0000555555748dfb in rb_parser_reg_compile (p=0x555555d1f760, str=93825000046904, options=0) at parse.y:12157
ruby#19 0x00005555557581c3 in parser_reg_compile (p=0x555555d1f760, str=93825000046904, options=0) at parse.y:12151
#20 0x00005555557580ac in reg_compile (p=0x555555d1f760, str=93825000046904, options=0) at parse.y:12167
ruby#21 0x0000555555746ebb in new_regexp (p=0x555555d1f760, node=0x555555dece68, options=0, loc=0x7fffffff89e8) at parse.y:10072
ruby#22 0x000055555573d1f5 in ruby_yyparse (p=0x555555d1f760) at parse.y:4395
ruby#23 0x000055555574a582 in yycompile0 (arg=93825000404832) at parse.y:5945
ruby#24 0x00005555558c6898 in rb_suppress_tracing (func=0x55555574a470 <yycompile0>, arg=93825000404832) at vm_trace.c:427
ruby#25 0x0000555555748290 in yycompile (vparser=93824999283456, p=0x555555d1f760, fname=93824999283624, line=1) at parse.y:5994
ruby#26 0x00005555557481ae in rb_parser_compile_file_path (vparser=93824999283456, fname=93824999283624, file=93824999283400, start=1) at parse.y:6098
ruby#27 0x00005555557cdd35 in load_file_internal (argp_v=140737488331760) at ruby.c:2023
ruby#28 0x00005555556438c5 in rb_ensure (b_proc=0x5555557cd610 <load_file_internal>, data1=140737488331760, e_proc=0x5555557cddd0 <restore_load_file>, data2=140737488331760) at eval.c:1128
ruby#29 0x00005555557cb68b in load_file (parser=93824999283456, fname=93824999283624, f=93824999283400, script=0, opt=0x7fffffffa468) at ruby.c:2142
ruby#30 0x00005555557cb339 in rb_parser_load_file (parser=93824999283456, fname_v=93824999283624) at ruby.c:2164
ruby#31 0x00005555556ba3e1 in load_iseq_eval (ec=0x555555c0a650, fname=93824999283624) at load.c:579
ruby#32 0x00005555556b857a in require_internal (ec=0x555555c0a650, fname=93824999284352, exception=1) at load.c:1016
ruby#33 0x00005555556b7967 in rb_require_string (fname=93824999284464) at load.c:1105
ruby#34 0x00005555556b7939 in rb_f_require (obj=93824999994824, fname=93824999284464) at load.c:811
ruby#35 0x00005555558b7ae0 in call_cfunc_1 (recv=93824999994824, argc=1, argv=0x7ffff7ecd0a8, func=0x5555556b7920 <rb_f_require>) at vm_insnhelper.c:2348
ruby#36 0x00005555558a8889 in vm_call_cfunc_with_frame (ec=0x555555c0a650, reg_cfp=0x7ffff7fccfa0, calling=0x7fffffffaab0, cd=0x555555d76a10, empty_kw_splat=0) at vm_insnhelper.c:2513
ruby#37 0x000055555589fb5c in vm_call_cfunc (ec=0x555555c0a650, reg_cfp=0x7ffff7fccfa0, calling=0x7fffffffaab0, cd=0x555555d76a10) at vm_insnhelper.c:2538
ruby#38 0x000055555589f22e in vm_call_method_each_type (ec=0x555555c0a650, cfp=0x7ffff7fccfa0, calling=0x7fffffffaab0, cd=0x555555d76a10) at vm_insnhelper.c:2924
ruby#39 0x000055555589ef47 in vm_call_method (ec=0x555555c0a650, cfp=0x7ffff7fccfa0, calling=0x7fffffffaab0, cd=0x555555d76a10) at vm_insnhelper.c:3038
ruby#40 0x0000555555866dbd in vm_call_general (ec=0x555555c0a650, reg_cfp=0x7ffff7fccfa0, calling=0x7fffffffaab0, cd=0x555555d76a10) at vm_insnhelper.c:3075
ruby#41 0x00005555558ae557 in vm_sendish (ec=0x555555c0a650, reg_cfp=0x7ffff7fccfa0, cd=0x555555d76a10, block_handler=0, method_explorer=0x5555558ae5d0 <vm_search_method_wrap>) at vm_insnhelper.c:4021
ruby#42 0x000055555587745b in vm_exec_core (ec=0x555555c0a650, initial=0) at insns.def:801
ruby#43 0x0000555555899b9c in rb_vm_exec (ec=0x555555c0a650, mjit_enable_p=1) at vm.c:1907
ruby#44 0x000055555589aaf0 in rb_iseq_eval_main (iseq=0x555555c1da80) at vm.c:2166
ruby#45 0x0000555555641f0b in rb_ec_exec_node (ec=0x555555c0a650, n=0x555555c1da80) at eval.c:277
ruby#46 0x0000555555641d62 in ruby_run_node (n=0x555555c1da80) at eval.c:335
ruby#47 0x000055555557a188 in main (argc=11, argv=0x7fffffffc848) at main.c:50
(gdb) fr 7
#7  0x0000555555666987 in newobj_init (klass=93824999964192, flags=5, v1=0, v2=0, v3=0, wb_protected=1, objspace=0x555555c0a1c0, obj=93825000456096) at gc.c:2134
2134        if (rgengc_remembered(objspace, (VALUE)obj)) rb_bug("newobj: %s is remembered.", obj_info(obj));
(gdb) p ((struct RVALUE*)obj)->file
$1 = 0x65a5992b0fb25ce7 <error: Cannot access memory at address 0x65a5992b0fb25ce7>
(gdb)
```

gc.c

@@ -2113,11 +2113,20 @@ newobj_init(VALUE klass, VALUE flags, VALUE v1, VALUE v2, VALUE v3, int wb_prote
 #endif
 
     /* OBJSETUP */
-    RBASIC(obj)->flags = flags;
-    RBASIC_SET_CLASS_RAW(obj, klass);
-    RANY(obj)->as.values.v1 = v1;
-    RANY(obj)->as.values.v2 = v2;
-    RANY(obj)->as.values.v3 = v3;
+    struct RVALUE buf = {
+        .as = {
+            .values =  {
+                .basic = {
+                    .flags = flags,
+                    .klass = klass,
+                },
+                .v1 = v1,
+                .v2 = v2,
+                .v3 = v3,
+            },
+        },
+    };
+    MEMCPY(RANY(obj), &buf, RVALUE, 1);
 
 #if RGENGC_CHECK_MODE
     GC_ASSERT(RVALUE_MARKED(obj) == FALSE);