Reset opencl flags if not detected to prevent build failure without opencl.
diff --git a/configure.ac b/configure.ac
index c5cf3b0..95ce0f0 100644
--- a/configure.ac
+++ b/configure.ac
@@ -126,6 +126,9 @@ if test "x$opencl" != xno; then
found_opencl=0])
LIBS=$SAVED_LIBS
CFLAGS=$SAVED_CFLAGS
+else
+ OPENCL_FLAGS=""
+ OPENCL_LIBS=""
fi
AC_CHECK_LIB(pthread, pthread_create, ,