Move function to reduce diff vs. upstream.

This is pretty trivial, but every little helps.

src/backend/storage/file/fd.c

@@ -1342,28 +1342,6 @@ FileSync(File file)
 	return returnCode;
 }
 
-/*
- * Get the size of a physical file by using fstat()
- *
- * Returns size in bytes if successful, < 0 otherwise
- */
-int64
-FileDiskSize(File file)
-{
-	int returnCode = 0;
-
-	returnCode = FileAccess(file);
-	if (returnCode < 0)
-		return returnCode;
-
-	struct stat buf;
-	returnCode = fstat(VfdCache[file].fd, &buf);
-	if (returnCode < 0)
-		return returnCode;
-
-	return (int64) buf.st_size;
-}
-
 int64
 FileSeek(File file, int64 offset, int whence)
 {
@@ -1427,6 +1405,28 @@ FileSeek(File file, int64 offset, int whence)
 	return VfdCache[file].seekPos;
 }
 
+/*
+ * Get the size of a physical file by using fstat()
+ *
+ * Returns size in bytes if successful, < 0 otherwise
+ */
+int64
+FileDiskSize(File file)
+{
+	int			returnCode = 0;
+	struct stat buf;
+
+	returnCode = FileAccess(file);
+	if (returnCode < 0)
+		return returnCode;
+
+	returnCode = fstat(VfdCache[file].fd, &buf);
+	if (returnCode < 0)
+		return returnCode;
+
+	return (int64) buf.st_size;
+}
+
 int64
 FileNonVirtualCurSeek(File file)
 {