Split out rmgr rm_desc functions into their own files

This is necessary (but not sufficient) to have them compilable outside
of a backend environment.

src/backend/access/rmgrdesc/standbydesc.c

@@ -0,0 +1,65 @@
+/*-------------------------------------------------------------------------
+ *
+ * standbydesc.c
+ *    rmgr descriptor routines for storage/ipc/standby.c
+ *
+ * Portions Copyright (c) 1996-2012, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ *    src/backend/access/rmgrdesc/standbydesc.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "storage/standby.h"
+
+static void
+standby_desc_running_xacts(StringInfo buf, xl_running_xacts *xlrec)
+{
+	int			i;
+
+	appendStringInfo(buf, " nextXid %u latestCompletedXid %u oldestRunningXid %u",
+					 xlrec->nextXid,
+					 xlrec->latestCompletedXid,
+					 xlrec->oldestRunningXid);
+	if (xlrec->xcnt > 0)
+	{
+		appendStringInfo(buf, "; %d xacts:", xlrec->xcnt);
+		for (i = 0; i < xlrec->xcnt; i++)
+			appendStringInfo(buf, " %u", xlrec->xids[i]);
+	}
+
+	if (xlrec->subxid_overflow)
+		appendStringInfo(buf, "; subxid ovf");
+}
+
+void
+standby_desc(StringInfo buf, uint8 xl_info, char *rec)
+{
+	uint8		info = xl_info & ~XLR_INFO_MASK;
+
+	if (info == XLOG_STANDBY_LOCK)
+	{
+		xl_standby_locks *xlrec = (xl_standby_locks *) rec;
+		int			i;
+
+		appendStringInfo(buf, "AccessExclusive locks:");
+
+		for (i = 0; i < xlrec->nlocks; i++)
+			appendStringInfo(buf, " xid %u db %u rel %u",
+							 xlrec->locks[i].xid, xlrec->locks[i].dbOid,
+							 xlrec->locks[i].relOid);
+	}
+	else if (info == XLOG_RUNNING_XACTS)
+	{
+		xl_running_xacts *xlrec = (xl_running_xacts *) rec;
+
+		appendStringInfo(buf, " running xacts:");
+		standby_desc_running_xacts(buf, xlrec);
+	}
+	else
+		appendStringInfo(buf, "UNKNOWN");
+}