doc/Makefile.am: deal with cases when stat and date commands fails by inserting 'unknown_date' in version.texi file

doc/Makefile.am

@@ -47,15 +47,19 @@ AM_MAKEINFOHTMLFLAGS = --css-include=$(top_srcdir)/doc/starpu.css --no-headers -
 uninstall-local:
 	$(RM) $(DESTDIR)$(infodir)/dir
 
-#TODO: when stat is not available on the machine, insert "unknown date"
 chapters/version.texi:
-	@for f in $(starpu_TEXINFOS) ; do \
-                if test -f $(top_srcdir)/doc/$$f ; then stat --format=%Y $(top_srcdir)/doc/$$f ; fi \
+	@-for f in $(starpu_TEXINFOS) ; do \
+                if test -f $(top_srcdir)/doc/$$f ; then stat --format=%Y $(top_srcdir)/doc/$$f 2>/dev/null ; fi \
         done | sort -r | head -1 > timestamp
-	@LC_ALL=C date --date=@`cat timestamp` +"%d %B %Y" > timestamp_updated
-	@LC_ALL=C date --date=@`cat timestamp` +"%B %Y" > timestamp_updated_month
-	@echo "@set UPDATED " `cat timestamp_updated` > $(top_srcdir)/doc/chapters/version.texi
-	@echo "@set UPDATED-MONTH" `cat timestamp_updated_month` >> $(top_srcdir)/doc/chapters/version.texi
+	@-LC_ALL=C date --date=@`cat timestamp` +"%d %B %Y" > timestamp_updated 2>/dev/null
+	@-LC_ALL=C date --date=@`cat timestamp` +"%B %Y" > timestamp_updated_month 2>/dev/null
+	@if test -s timestamp_updated ; then \
+		echo "@set UPDATED " `cat timestamp_updated` > $(top_srcdir)/doc/chapters/version.texi;\
+		echo "@set UPDATED-MONTH" `cat timestamp_updated_month` >> $(top_srcdir)/doc/chapters/version.texi;\
+	else \
+		echo "@set UPDATED unknown_date" > $(top_srcdir)/doc/chapters/version.texi ;\
+		echo "@set UPDATED-MONTH unknown_date" >> $(top_srcdir)/doc/chapters/version.texi; \
+	fi
 	@echo "@set EDITION $(VERSION)" >> $(top_srcdir)/doc/chapters/version.texi
 	@echo "@set VERSION $(VERSION)" >> $(top_srcdir)/doc/chapters/version.texi
 	@$(RM) timestamp timestamp_updated timestamp_updated_month