configure: use -iquote for non-system include paths#7169

hjelmn merged 2 commits intoopen-mpi:masteropen-mpi/ompi:masterfrom

hjelmn:fix_what_wg21_calls_our_problem_not_theirs_seriously__in_some_ways_they_are_correct_but_wtfhjelmn/ompi:fix_what_wg21_calls_our_problem_not_theirs_seriously__in_some_ways_they_are_correct_but_wtfCopy head branch name to clipboard