[doc] Add "--disable-doc" to configure

Configure option "--disable-doc" will prevent building
the documents under doc. Saves build time and the need to
have document building tools installed. Useful when your build
machine is different from your development machine.

Makefile.am

@@ -1,7 +1,7 @@
 ## Process this file with automake to produce Makefile.in.
 
 SUBDIRS = lib @ZEBRA@ @BGPD@ @RIPD@ @RIPNGD@ @OSPFD@ @OSPF6D@ \
-         @ISISD@ @WATCHQUAGGA@ @VTYSH@ @OSPFCLIENT@ doc m4 @pkgsrcdir@ \
+         @ISISD@ @WATCHQUAGGA@ @VTYSH@ @OSPFCLIENT@ @DOC@ m4 @pkgsrcdir@ \
          redhat @SOLARIS@
 
 DIST_SUBDIRS = lib zebra bgpd ripd ripngd ospfd ospf6d \

configure.ac

@@ -185,6 +185,8 @@ AC_ARG_ENABLE(vtysh,
 [  --enable-vtysh          include integrated vty shell for Quagga])
 AC_ARG_ENABLE(ipv6,
 [  --disable-ipv6          turn off IPv6 related features and daemons])
+AC_ARG_ENABLE(doc,
+[  --disable-doc           do not build docs])
 AC_ARG_ENABLE(zebra,
 [  --disable-zebra         do not build zebra daemon])
 AC_ARG_ENABLE(bgpd,
@@ -1154,6 +1156,13 @@ QUAGGA_INCLUDES
 #endif
 ])dnl
 
+dnl disable doc check
+if test "${enable_doc}" = "no";then
+  DOC=""
+else
+  DOC="doc"
+fi
+
 dnl --------------------
 dnl Daemon disable check
 dnl --------------------
@@ -1230,6 +1239,7 @@ else
   AC_DEFINE(DISABLE_BGP_ANNOUNCE,0,Disable BGP installation to zebra)
 fi
 
+AC_SUBST(DOC)
 AC_SUBST(ZEBRA)
 AC_SUBST(BGPD)
 AC_SUBST(RIPD)