fix unaligned access in ParseCommitRecord

Author: kelvich

src/backend/access/rmgrdesc/xactdesc.c

@@ -97,10 +97,10 @@ ParseCommitRecord(uint8 info, xl_xact_commit *xlrec, xl_xact_parsed_commit *pars
 
 	if (parsed->xinfo & XACT_XINFO_HAS_TWOPHASE)
 	{
-		xl_xact_twophase *xl_twophase = (xl_xact_twophase *) data;
-
-		parsed->twophase_xid = xl_twophase->xid;
+		xl_xact_twophase xl_twophase;
 
+		memcpy(&xl_twophase, data, sizeof(xl_twophase));
+		parsed->twophase_xid = xl_twophase.xid;
 		data += sizeof(xl_xact_twophase);
 
 		if (parsed->xinfo & XACT_XINFO_HAS_GID)