Don't try to build manpages if asciidoc is missing

Commit f9157fd changed the rules for
the documentation, so make always tried to build it and failed if
asciidoc was missing since that commit.

Now configure tests whether asciidoc is available and builds the
documentation conditionally. It also reports that to the user.

Signed-off-by: Stefan Weil <sw@weilnetz.de>

configure.ac

@@ -414,6 +414,17 @@ AC_SYS_LARGEFILE
 
 AC_CHECK_FUNCS([getline])
 
+# ----------------------------------------
+# Check for programs needed to build documentation.
+# ----------------------------------------
+
+AC_CHECK_PROG([have_asciidoc], asciidoc, true, false)
+if $have_asciidoc; then
+  AM_CONDITIONAL([ASCIIDOC], true)
+else
+  AM_CONDITIONAL([ASCIIDOC], false)
+fi
+
 # ----------------------------------------
 # Checks for typedefs, structures, and compiler characteristics.
 # ----------------------------------------
@@ -513,6 +524,16 @@ echo "You can now build and install $PACKAGE_NAME by running:"
 echo ""
 echo "$ make"
 echo "$ sudo make install"
+echo ""
+
+AM_COND_IF([ASCIIDOC],
+  [
+   echo "This will also build the documentation."
+  ], [
+   echo "Documentation will not be built because asciidoc is missing."
+  ]
+)
+
 # echo "$ sudo make install LANGS=\"eng ara deu\""
 # echo "  Or:"
 # echo "$ sudo make install-langs"

doc/Makefile.am

@@ -1,5 +1,7 @@
 # doc/Makefile.am
 
+if ASCIIDOC
+
 asciidoc=asciidoc -d manpage
 
 man_MANS = \
@@ -28,3 +30,5 @@ man_MANS = \
 	$(asciidoc) -o $@ $<
 
 MAINTAINERCLEANFILES = $(man_MANS) Doxyfile
+
+endif