Erase the magic number in the trx sys header using a redo-logged write;

it should be redo-logged because the data structure is file-based;
this patch does not fix any bug; the original erase operation was added
in r781 to fix Valgrind Bug #20791

trx/trx0sys.c

@@ -847,12 +847,6 @@ trx_sysf_create(
 			   mtr);
 	ut_a(buf_frame_get_page_no(page) == TRX_SYS_PAGE_NO);
 
-	/* Reset the doublewrite buffer magic number to zero so that we
-	know that the doublewrite buffer has not yet been created (this
-	suppresses a Valgrind warning) */
-
-	mach_write_to_4(page + TRX_SYS_DOUBLEWRITE + TRX_SYS_DOUBLEWRITE_MAGIC,
-			0);
 #ifdef UNIV_SYNC_DEBUG
 	buf_page_dbg_add_level(page, SYNC_TRX_SYS_HEADER);
 #endif /* UNIV_SYNC_DEBUG */
@@ -860,6 +854,13 @@ trx_sysf_create(
 	mlog_write_ulint(page + FIL_PAGE_TYPE, FIL_PAGE_TYPE_TRX_SYS,
 			 MLOG_2BYTES, mtr);
 
+	/* Reset the doublewrite buffer magic number to zero so that we
+	know that the doublewrite buffer has not yet been created (this
+	suppresses a Valgrind warning) */
+
+	mlog_write_ulint(page + TRX_SYS_DOUBLEWRITE
+			 + TRX_SYS_DOUBLEWRITE_MAGIC, 0, MLOG_4BYTES, mtr);
+
 	sys_header = trx_sysf_get(mtr);
 
 	/* Start counting transaction ids from number 1 up */