man: Make the manpages reproducible

Whilst working on the Reproducible Builds effort [0], we noticed
that corosync could not be built reproducibly.

This is because, whilst it uses SOURCE_DATE_EPOCH[1], the output
varies depending on the current timezone.

(The LC_ALL is not needed as we only use %Y-%m-%d)

This was originally filed in Debian as #896441.

 [0] https://reproducible-builds.org/
 [1] https://reproducible-builds.org/specs/source-date-epoch/
 [2] https://bugs.debian.org/896441

Signed-off-by: Chris Lamb <lamby@debian.org>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>

man/Makefile.am

@@ -149,7 +149,9 @@ HTML_DOCS 		= $(dist_man_MANS:%=%.html) $(man_MANS:%=%.html)
 %.3: %.3.in $(autogen_common)
 	@echo Generating $@ man page && \
 	rm -f $@-t-t $@-t $@ && \
-	date="$$(LC_ALL=C date "+%F" $${SOURCE_DATE_EPOCH+-d @$$SOURCE_DATE_EPOCH})" && \
+	DATE_FMT="%Y-%m-%d" && \
+	SOURCE_DATE_EPOCH="$${SOURCE_DATE_EPOCH:-$$(date +%s)}" && \
+	date="$$(date -u -d "@$$SOURCE_DATE_EPOCH" "+$$DATE_FMT" 2>/dev/null || date -u -r "$$SOURCE_DATE_EPOCH" "+$$DATE_FMT" 2>/dev/null || date -u "+$$DATE_FMT")" && \
 	awk "{print}(\$$1 ~ /@COMMONIPCERRORS@/){exit 0}" ${top_srcdir}/man/$@.in > $@-t-t && \
 	cat ${top_srcdir}/man/$(autogen_common) >> $@-t-t && \
 	awk -v p=0 "(\$$1 ~ /@COMMONIPCERRORS@/){p = 1} {if(p==1)print}" ${top_srcdir}/man/$@.in >> $@-t-t && \