[ruby/json] Enable JSON_DEBUG for parser/extconf.rb

ruby/json@3ea744ad67

Author: byroot

ext/json/parser/extconf.rb

@@ -1,6 +1,7 @@
 # frozen_string_literal: true
 require 'mkmf'
 
+$defs << "-DJSON_DEBUG" if ENV["JSON_DEBUG"]
 have_func("rb_enc_interned_str", "ruby/encoding.h") # RUBY_VERSION >= 3.0
 have_func("rb_hash_new_capa", "ruby.h") # RUBY_VERSION >= 3.2
 have_func("rb_hash_bulk_insert", "ruby.h") # Missing on TruffleRuby