The external include path might be empty e.g. if the relevant headers are to be
found directly in the MinGW sysroot, but we still don't want to use the bundled
library's include path in that case.
Signed-off-by: Zebediah Figura <zfigura@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>