build: revert recent change with distributed man page handling

* man/local.mk: commit f114495e added an extra check to ensure
a binary was working before using it to generate the man page.
However this was not working for the false(1) command,
and also one can generally specify that one should not
be using generated commands on the current system by passing
'cross_compiling=yes' to the configure invocation.

man/local.mk

@@ -191,16 +191,9 @@ endif
 	  && $(MKDIR_P) $$t						\
 	  && (cd $$t && $(LN_S) '$(abs_top_builddir)/src/'$$prog$(EXEEXT) \
 				$$argv$(EXEEXT))			\
-	  || exit 1;							\
-## Double-check whether the built binary succeeds with --help as the above
-## CROSS_COMPILING condition might have been wrong in some cases, e.g. when
-## building against an incompatible glibc version on the same platform.
-	$$t/$$argv$(EXEEXT) --help </dev/null >/dev/null		\
-	  && run_help2man="$(run_help2man)"				\
-	  || run_help2man="$(srcdir)/man/dummy-man";			\
-	: $${SOURCE_DATE_EPOCH=`cat $(srcdir)/.timestamp 2>/dev/null || :`} \
+	&& : $${SOURCE_DATE_EPOCH=`cat $(srcdir)/.timestamp 2>/dev/null || :`} \
 	&& : $${TZ=UTC0} && export TZ					\
-	&& export SOURCE_DATE_EPOCH && $${run_help2man}			\
+	&& export SOURCE_DATE_EPOCH && $(run_help2man)			\
 		     --source='$(PACKAGE_STRING)'			\
 		     --include=$(srcdir)/man/$$name.x			\
 		     --output=$$t/$$name.1				\