configure: add has_or_warn

By popular request, add a function to only warn on missing stuff.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 reporter_name="Bart vdr. Meulen <bartvdrmeulen@gmail.com>"

 reporter_url=""

 reporter_comment="Config to build cross-compiler with mingw as kernel type"