Silence minor compiler warnings.

Depending on compiler version and optimization level, we might
get a complaint that lazy_scan_heap's "freespace" is used
uninitialized.

Compilers not aware that ereport(ERROR) doesn't return complained
about bbsink_lz4_new().

Assigning "-1" to a uint64 value has unportable results; fortunately,
the value of xlogreadsegno is unimportant when xlogreadfd is -1.
(It looks to me like there is no need for xlogreadsegno to be static
in the first place, but I didn't venture to change that.)

src/backend/access/heap/vacuumlazy.c

@@ -1112,7 +1112,7 @@ lazy_scan_heap(LVRelState *vacrel, int nworkers)
 			if (lazy_scan_noprune(vacrel, buf, blkno, page, &hastup,
 								  &recordfreespace))
 			{
-				Size		freespace;
+				Size		freespace = 0;
 
 				/*
 				 * Processed page successfully (without cleanup lock) -- just

src/backend/replication/basebackup_lz4.c

@@ -66,6 +66,7 @@ bbsink_lz4_new(bbsink *next, int compresslevel)
 	ereport(ERROR,
 			(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
 			 errmsg("lz4 compression is not supported by this build")));
+	return NULL;				/* keep compiler quiet */
 #else
 	bbsink_lz4 *sink;
 

src/bin/pg_rewind/parsexlog.c

@@ -38,7 +38,7 @@ static const char *RmgrNames[RM_MAX_ID + 1] = {
 static void extractPageInfo(XLogReaderState *record);
 
 static int	xlogreadfd = -1;
-static XLogSegNo xlogreadsegno = -1;
+static XLogSegNo xlogreadsegno = 0;
 static char xlogfpath[MAXPGPATH];
 
 typedef struct XLogPageReadPrivate