build: add empty config.h for windows

config.h is automatically generated by autoheader on Linux on
configure time. For Windows there needs to be one that could
be included, otherwise the build faild on #include <config.h>

Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
diff --git a/config.h b/config.h
new file mode 100644
index 0000000..3b5173f
--- /dev/null
+++ b/config.h
@@ -0,0 +1 @@
+/* Empty config.h. for windows build */