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, 4 insertions, 0 deletions

diff --git a/process.c b/process.c
index 8abb3ea86f..90db3c5677 100644
--- a/process.c
+++ b/process.c
@@ -8445,6 +8445,10 @@ InitVM_process(void)
 #define rb_intern(str) rb_intern_const(str)
     rb_define_virtual_variable("$?", get_CHILD_STATUS, 0);
     rb_define_virtual_variable("$$", get_PROCESS_ID, 0);
+
+    rb_gvar_ractor_local("$$");
+    rb_gvar_ractor_local("$?");
+
     rb_define_global_function("exec", f_exec, -1);
     rb_define_global_function("fork", rb_f_fork, 0);
     rb_define_global_function("exit!", rb_f_exit_bang, -1);