RJIT: Fix a typo

and import a missing function

lib/ruby_vm/rjit/insn_compiler.rb

@@ -64,7 +64,7 @@ module RubyVM::RJIT
       when :setn then setn(jit, ctx, asm)
       when :adjuststack then adjuststack(jit, ctx, asm)
       when :defined then defined(jit, ctx, asm)
-      when :definedvar then definedivar(jit, ctx, asm)
+      when :definedivar then definedivar(jit, ctx, asm)
       # checkmatch
       # checkkeyword
       # checktype

rjit_c.rb

@@ -521,6 +521,10 @@ module RubyVM::RJIT # :nodoc: all
     Primitive.cexpr! %q{ SIZET2NUM((size_t)rb_hash_new_with_size) }
   end
 
+  def C.rb_ivar_defined
+    Primitive.cexpr! %q{ SIZET2NUM((size_t)rb_ivar_defined) }
+  end
+
   def C.rb_ivar_get
     Primitive.cexpr! %q{ SIZET2NUM((size_t)rb_ivar_get) }
   end

tool/rjit/bindgen.rb

@@ -513,6 +513,7 @@ generator = BindingGenerator.new(
     rjit_optimized_call
     rjit_str_neq_internal
     rjit_record_exit_stack
+    rb_ivar_defined
   ],
   types: %w[
     CALL_DATA