configure: more properly disable header when check_header_oc() fails

This should make no difference currently

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
configure: use TMPM in check_header_oc

Some compilers when given -x objective-c will tell that they dont support
that but return success. Using a .m file instead returns proper failure in
that case

This should fix a build failure on freebsd

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>