RJIT: Fix unwanted shadowing in set_local_type

local_idx should not be overwritten.

bootstraptest/test_rjit.rb

@@ -42,3 +42,17 @@ assert_equal '1', %q{
 
   entry
 }
+
+# Updating local type in Context
+assert_normal_exit %q{
+  def foo(flag, object)
+    klass = if flag
+      object
+    end
+    klass ||= object
+    return klass.new
+  end
+
+  foo(false, Object)
+  foo(true, Object)
+}

lib/ruby_vm/rjit/context.rb

@@ -264,9 +264,9 @@ module RubyVM::RJIT
           # noop
         in MapToSelf
           # noop
-        in MapToLocal[local_idx]
-          if stack_idx == local_idx
-            self.temp_types[stack_idx] = self.local_types[local_idx];
+        in MapToLocal[temp_local_idx]
+          if stack_idx == temp_local_idx
+            self.temp_types[stack_idx] = self.local_types[temp_local_idx]
             self.temp_mapping[stack_idx] = MapToStack
           else
             # noop