Added configure check for libutil.h.

diff --git a/configure.in b/configure.in
index 09aabf5..cc61c9a 100644
--- a/configure.in
+++ b/configure.in
@@ -694,6 +694,7 @@
 	elf.h \
 	float.h \
 	libio.h \
+	libutil.h \
 	link.h \
 	linux/cdrom.h \
 	linux/joystick.h \