Building pg_xlogdump reproducibly

The list of objects used to link pg_xlogdump is coming from
$(wildcard *desc.c) which returns them in filesystem order. This makes
the build result depend on this ordering, yielding different
compilation results.

This patch fixes the reproducibility issue:

--- a/src/bin/pg_xlogdump/Makefile
+++ b/src/bin/pg_xlogdump/Makefile
@@ -12,7 +12,7 @@ OBJS = pg_xlogdump.o compat.o xlogreaderoverride CPPFLAGS := -DFRONTEND $(CPPFLAGS)
-RMGRDESCSOURCES = $(notdir $(wildcard $(top_srcdir)/src/backend/access/rmgrdesc/*desc.c))
+RMGRDESCSOURCES = $(sort $(notdir $(wildcard $(top_srcdir)/src/backend/access/rmgrdesc/*desc.c)))RMGRDESCOBJS =
$(patsubst%.c,%.o,$(RMGRDESCSOURCES))
 

Spotted by Debian's reproducible builds project:
https://wiki.debian.org/ReproducibleBuilds
https://reproducible-builds.org/

Christoph