[Feature #17684] Declare --disable-gems is for debugging

ruby.c

@@ -303,7 +303,7 @@ usage(const char *name, int help, int highlight, int columns)
 	M("--copyright",                            "", "print the copyright"),
 	M("--dump={insns|parsetree|...}[,...]",     "",
           "dump debug information. see below for available dump list"),
-	M("--enable={gems|rubyopt|...}[,...]", ", --disable={gems|rubyopt|...}[,...]",
+	M("--enable={jit|rubyopt|...}[,...]", ", --disable={jit|rubyopt|...}[,...]",
 	  "enable or disable features. see below for available features"),
 	M("--external-encoding=encoding",           ", --internal-encoding=encoding",
 	  "specify the default external or internal character encoding"),
@@ -319,7 +319,7 @@ usage(const char *name, int help, int highlight, int columns)
 	M("parsetree_with_comment", "", "AST with comments"),
     };
     static const struct message features[] = {
-	M("gems",    "",        "rubygems (default: "DEFAULT_RUBYGEMS_ENABLED")"),
+	M("gems",    "",        "rubygems (only for debugging, default: "DEFAULT_RUBYGEMS_ENABLED")"),
 	M("did_you_mean", "",   "did_you_mean (default: "DEFAULT_RUBYGEMS_ENABLED")"),
 	M("rubyopt", "",        "RUBYOPT environment variable (default: enabled)"),
 	M("frozen-string-literal", "", "freeze all string literals (default: disabled)"),