Fix include path to point to sysroot

Change-Id: I48cecd04f1523cc45e52db614c8a47d621a0b0ef
diff --git a/configure.ac b/configure.ac
index f826305..e77b4f2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -14,6 +14,9 @@
 AC_PROG_LIBTOOL
 AC_PROG_CXX
 
+PKG_CHECK_MODULES([LIBXML], [libxml-2.0])
+AC_SUBST([LIBXML_CFLAGS])
+AC_SUBST([LIBXML_LIBS])
 
 # Checks for libraries.