Install systemd services with autotools

Change-Id: I103bf3468d53578045593eac31b61f7e0248495e
diff --git a/configure.ac b/configure.ac
index c233fa3..73b6dce 100644
--- a/configure.ac
+++ b/configure.ac
@@ -176,6 +176,22 @@
 AC_MSG_RESULT([$enable_ext_tests])
 AM_CONDITIONAL(ENABLE_EXT_TESTS, test "x$enable_ext_tests" = "xyes")
 
+# https://www.freedesktop.org/software/systemd/man/daemon.html
+AC_ARG_WITH([systemdsystemunitdir],
+     [AS_HELP_STRING([--with-systemdsystemunitdir=DIR], [Directory for systemd service files])],,
+     [with_systemdsystemunitdir=auto])
+AS_IF([test "x$with_systemdsystemunitdir" = "xyes" -o "x$with_systemdsystemunitdir" = "xauto"], [
+     def_systemdsystemunitdir=$($PKG_CONFIG --variable=systemdsystemunitdir systemd)
+
+     AS_IF([test "x$def_systemdsystemunitdir" = "x"],
+   [AS_IF([test "x$with_systemdsystemunitdir" = "xyes"],
+    [AC_MSG_ERROR([systemd support requested but pkg-config unable to query systemd package])])
+    with_systemdsystemunitdir=no],
+   [with_systemdsystemunitdir="$def_systemdsystemunitdir"])])
+AS_IF([test "x$with_systemdsystemunitdir" != "xno"],
+      [AC_SUBST([systemdsystemunitdir], [$with_systemdsystemunitdir])])
+AM_CONDITIONAL([HAVE_SYSTEMD], [test "x$with_systemdsystemunitdir" != "xno"])
+
 AC_MSG_RESULT([CFLAGS="$CFLAGS"])
 AC_MSG_RESULT([CPPFLAGS="$CPPFLAGS"])
 
@@ -201,4 +217,6 @@
     tests/v42bis/Makefile
     doc/Makefile
     doc/examples/Makefile
+    contrib/Makefile
+    contrib/systemd/Makefile
     Makefile)