add doc/man to subdir if configure flag --enable-man is set

Makefile.am

@@ -1,5 +1,8 @@
 ACLOCAL_AMFLAGS = -I build-aux/m4
 SUBDIRS = src
+if ENABLE_MAN
+SUBDIRS += doc/man
+endif
 .PHONY: deploy FORCE
 
 GZIP_ENV="-9n"
@@ -280,5 +283,7 @@ CLEANFILES = $(OSX_DMG) $(BITCOIN_WIN_INSTALLER)
 
 .INTERMEDIATE: $(COVERAGE_INFO)
 
+DISTCHECK_CONFIGURE_FLAGS = --enable-man
+
 clean-local:
 	rm -rf test_bitcoin.coverage/ zcash-gtest.coverage/ total.coverage/ $(OSX_APP)