Try to avoid compiler warnings in optimized builds.

Per report from Andres Freund, who also says that this fix
works for him.

Discussion: http://postgr.es/m/20200405193118.alprgmozhxcfabkw@alap3.anarazel.de

src/bin/pg_verifybackup/parse_manifest.h

@@ -29,7 +29,8 @@ typedef void (*json_manifest_perwalrange_callback)(JsonManifestParseContext *,
 								 TimeLineID tli,
 								 XLogRecPtr start_lsn, XLogRecPtr end_lsn);
 typedef void (*json_manifest_error_callback)(JsonManifestParseContext *,
-								 char *fmt, ...) pg_attribute_printf(2, 3);
+								 char *fmt, ...) pg_attribute_printf(2, 3)
+								 pg_attribute_noreturn();
 
 struct JsonManifestParseContext
 {