mod: Build system changes for dirauth module

Make our build system support a disable dirauth module option. It can only be
disabled explicitly with:

  $ ./configure --disable-module-dirauth

If *not* specified that is enabled, an automake conditional variable is set to
true and a defined value for the C code:

  AM_CONDITIONAL: BUILD_MODULE_DIRAUTH
  AC_DEFINE: HAVE_MODULE_DIRAUTH=1

This introduces the dirauth/ module directory in src/or/ for which .c files
are only compiled if the BUILD_MODULE_DIRAUTH is set.

All the header files are compiled in regardless of the support so we can use
the alternative entry point functions of the dirauth subsystem.

Signed-off-by: David Goulet <dgoulet@torproject.org>

configure.ac

@@ -230,6 +230,19 @@ if test "x$enable_android" = "xyes"; then
 
 fi
 
+dnl ---
+dnl Tor modules options. These options are namespaced with --disable-module-XXX
+dnl ---
+
+dnl Directory Authority module.
+AC_ARG_ENABLE([module-dirauth],
+              AS_HELP_STRING([--disable-module-dirauth],
+                             [Do not build tor with the dirauth module]),
+              [], dnl Action if-given
+              AC_DEFINE([HAVE_MODULE_DIRAUTH], [1],
+                        [Compile with Directory Authority feature support]))
+AM_CONDITIONAL(BUILD_MODULE_DIRAUTH, [test "x$enable_module_dirauth" != "xno"])
+
 dnl check for the correct "ar" when cross-compiling.
 dnl   (AM_PROG_AR was new in automake 1.11.2, which we do not yet require,
 dnl    so kludge up a replacement for the case where it isn't there yet.)

src/or/include.am

@@ -114,6 +114,16 @@ LIBTOR_A_SOURCES = \
 	src/or/onion_ntor.c				\
 	$(tor_platform_source)
 
+#
+# Modules are conditionnally compiled in tor starting here. We add the C files
+# only if the modules has been enabled at configure time.
+#
+
+# The Directory Authority module.
+if BUILD_MODULE_DIRAUTH
+#LIBTOR_A_SOURCES +=
+endif
+
 src_or_libtor_a_SOURCES = $(LIBTOR_A_SOURCES)
 src_or_libtor_testing_a_SOURCES = $(LIBTOR_A_SOURCES)
 
@@ -259,6 +269,12 @@ ORHEADERS = \
 	src/or/torcert.h				\
 	src/or/tor_api_internal.h
 
+# We add the headers of the modules even though they are disabled so we can
+# properly compiled the entry points stub.
+
+# The Directory Authority module headers.
+#ORHEADERS +=
+
 # This may someday want to be an installed file?
 noinst_HEADERS += src/or/tor_api.h