MJIT: Make it parsable by Solargraph (#6827)

* Revert "Revert "MJIT: Make it parsable by Solargraph""

This reverts commit 8e18761da1.

* Call rb_gc_register_mark_object

mjit.c

@@ -1324,7 +1324,7 @@ static VALUE rb_mMJIT = 0;
 // RubyVM::MJIT::C
 VALUE rb_mMJITC = 0;
 // RubyVM::MJIT::Compiler
-VALUE rb_mMJITCompiler = 0;
+VALUE rb_cMJITCompiler = 0;
 
 // [experimental] Call custom RubyVM::MJIT.compile if defined
 static void
@@ -1765,8 +1765,9 @@ mjit_init(const struct mjit_options *opts)
         mjit_enabled = false;
         return;
     }
-    rb_mMJITCompiler = rb_const_get(rb_mMJIT, rb_intern("Compiler"));
     rb_mMJITC = rb_const_get(rb_mMJIT, rb_intern("C"));
+    rb_cMJITCompiler = rb_funcall(rb_const_get(rb_mMJIT, rb_intern("Compiler")), rb_intern("new"), 0);
+    rb_gc_register_mark_object(rb_cMJITCompiler);
 
     mjit_call_p = true;
     mjit_pid = getpid();

mjit.rb

@@ -20,6 +20,7 @@ if RubyVM::MJIT.enabled?
     return # miniruby doesn't support MJIT
   end
 
+  RubyVM::MJIT::C = Object.new # forward declaration for mjit/compiler
   require "mjit/c_type"
   require "mjit/instruction"
   require "mjit/compiler"

mjit_c.rb

@@ -2,8 +2,6 @@
 # Part of this file is generated by tool/mjit/bindgen.rb.
 # Run `make mjit-bindgen` to update code between "MJIT bindgen begin" and "MJIT bindgen end".
 module RubyVM::MJIT
-  C = Object.new
-
   # This `class << C` section is for calling C functions. For importing variables
   # or macros as is, please consider using tool/mjit/bindgen.rb instead.
   class << C
@@ -769,4 +767,4 @@ module RubyVM::MJIT
   end
 
   ### MJIT bindgen end ###
-end if RubyVM::MJIT.enabled?
+end if RubyVM::MJIT.enabled? && RubyVM::MJIT.const_defined?(:C) # not defined for miniruby

mjit_compiler.c

@@ -122,8 +122,8 @@ mjit_compile(FILE *f, const rb_iseq_t *iseq, const char *funcname, int id)
     bool original_call_p = mjit_call_p;
     mjit_call_p = false; // Avoid impacting JIT metrics by itself
 
-    extern VALUE rb_mMJITCompiler;
-    VALUE src = rb_funcall(rb_mMJITCompiler, rb_intern("compile"), 3,
+    extern VALUE rb_cMJITCompiler;
+    VALUE src = rb_funcall(rb_cMJITCompiler, rb_intern("compile"), 3,
                            rb_ptr("rb_iseq_t", iseq), rb_str_new_cstr(funcname), INT2NUM(id));
     if (!NIL_P(src)) {
         fprintf(f, "%s", RSTRING_PTR(src));