Use global rb_intern strings instead of point of use

Author: sodabrew

ext/mysql2/client.c

@@ -18,10 +18,11 @@ VALUE cMysql2Client;
 extern VALUE mMysql2, cMysql2Error;
 static VALUE sym_id, sym_version, sym_async, sym_symbolize_keys, sym_as, sym_array, sym_stream;
 static ID intern_merge, intern_merge_bang, intern_error_number_eql, intern_sql_state_eql;
+static ID intern_brackets, intern_new;
 
 #ifndef HAVE_RB_HASH_DUP
 VALUE rb_hash_dup(VALUE other) {
-  return rb_funcall(rb_cHash, rb_intern("[]"), 1, other);
+  return rb_funcall(rb_cHash, intern_brackets, 1, other);
 }
 #endif
 
@@ -123,7 +124,7 @@ static VALUE rb_raise_mysql2_error(mysql_client_wrapper *wrapper) {
   rb_enc_associate(rb_sql_state, rb_usascii_encoding());
 #endif
 
-  e = rb_funcall(cMysql2Error, rb_intern("new"), 2, rb_error_msg, LONG2FIX(wrapper->server_version));
+  e = rb_funcall(cMysql2Error, intern_new, 2, rb_error_msg, LONG2FIX(wrapper->server_version));
   rb_funcall(e, intern_error_number_eql, 1, UINT2NUM(mysql_errno(wrapper->client)));
   rb_funcall(e, intern_sql_state_eql, 1, rb_sql_state);
   rb_exc_raise(e);
@@ -1305,6 +1306,8 @@ void init_mysql2_client() {
   sym_array           = ID2SYM(rb_intern("array"));
   sym_stream          = ID2SYM(rb_intern("stream"));
 
+  intern_brackets = rb_intern("[]");
+  intern_new = rb_intern("new");
   intern_merge = rb_intern("merge");
   intern_merge_bang = rb_intern("merge!");
   intern_error_number_eql = rb_intern("error_number=");