configure: add --disable-modules option

configure.ac

@@ -70,6 +70,10 @@ AC_ARG_ENABLE([daemon],
     AS_HELP_STRING([--disable-daemon], [Don't build Knot DNS main daemon]), [], [enable_daemon=yes])
 AM_CONDITIONAL([HAVE_DAEMON], [test "$enable_daemon" = "yes"])
 
+# Build Knot DNS modules
+AC_ARG_ENABLE([modules],
+    AS_HELP_STRING([--disable-modules], [Don't build Knot DNS modules]), [], [enable_modules=yes])
+
 # Build Knot DNS utilities
 AC_ARG_ENABLE([utilities],
     AS_HELP_STRING([--disable-utilities], [Don't build Knot DNS utilities]), [], [enable_utilities=yes])

m4/knot-module.m4

@@ -7,7 +7,10 @@ AC_DEFUN([KNOT_MODULE],
   AC_ARG_WITH([module-$1],
     AS_HELP_STRING([--with-module-$1=yes|shared|no], [Build '$1' module [default=$2]]),
     [module=$withval],
-    [module=$2]
+    AS_IF([test "$enable_modules" = "no"],
+      [module=no],
+      [module=$2]
+    )
   )
 
   doc_modules="${doc_modules}.. include:: modules/$1/$1.rst\n"