Correct out-of-tree builds for systemd workaround

Change-Id: I27c92f1b31da36a00585fa07376766a1f94e81df
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
diff --git a/configure.ac b/configure.ac
index 45d9c0e..2ad9855 100644
--- a/configure.ac
+++ b/configure.ac
@@ -8,7 +8,7 @@
 
 # Modify header template
 AH_TOP([#pragma once])
-AH_BOTTOM([#include "workaround/systemd.h"])
+AH_BOTTOM([#include "libmapper/workaround/systemd.h"])
 
 # Checks for programs.
 AC_PROG_CC