configure: Add check for valgrind/valgrind.h.
diff --git a/configure.ac b/configure.ac
index 457f32e..9aaacab 100644
--- a/configure.ac
+++ b/configure.ac
@@ -335,7 +335,8 @@
 	termios.h \
 	unistd.h \
 	utime.h \
-	valgrind/memcheck.h
+	valgrind/memcheck.h \
+	valgrind/valgrind.h
 )
 AC_HEADER_STAT()