Some global variables can be accessed from ractors

Some global variables should be used from non-main Ractors.
[Bug #17268]

```ruby
     # ractor-local (derived from created ractor): debug
     '$DEBUG' => $DEBUG,
     '$-d' => $-d,

     # ractor-local (derived from created ractor): verbose
     '$VERBOSE' => $VERBOSE,
     '$-w' => $-w,
     '$-W' => $-W,
     '$-v' => $-v,

     # process-local (readonly): other commandline parameters
     '$-p' => $-p,
     '$-l' => $-l,
     '$-a' => $-a,

     # process-local (readonly): getpid
     '$$'  => $$,

     # thread local: process result
     '$?'  => $?,

     # scope local: match
     '$~'  => $~.inspect,
     '$&'  => $&,
     '$`'  => $`,
     '$\''  => $',
     '$+'  => $+,
     '$1'  => $1,

     # scope local: last line
     '$_' => $_,

     # scope local: last backtrace
     '$@' => $@,
     '$!' => $!,

     # ractor local: stdin, out, err
     '$stdin'  => $stdin.inspect,
     '$stdout' => $stdout.inspect,
     '$stderr' => $stderr.inspect,
```

1 files changed, 7 insertions, 0 deletions

diff --git a/re.c b/re.c
index badd321782..020ba7b6d6 100644
--- a/re.c
+++ b/re.c
@@ -19,6 +19,7 @@
 #include "internal/imemo.h"
 #include "internal/re.h"
 #include "internal/string.h"
+#include "internal/variable.h"
 #include "regint.h"
 #include "ruby/encoding.h"
 #include "ruby/re.h"
@@ -4052,6 +4053,12 @@ Init_Regexp(void)
     rb_define_virtual_variable("$'", postmatch_getter, 0);
     rb_define_virtual_variable("$+", last_paren_match_getter, 0);
 
+    rb_gvar_ractor_local("$~");
+    rb_gvar_ractor_local("$&");
+    rb_gvar_ractor_local("$`");
+    rb_gvar_ractor_local("$'");
+    rb_gvar_ractor_local("$+");
+
     rb_define_virtual_variable("$=", ignorecase_getter, ignorecase_setter);
     rb_define_virtual_variable("$KCODE", kcode_getter, kcode_setter);
     rb_define_virtual_variable("$-K", kcode_getter, kcode_setter);