Mingw compile fix

• fix finding of bfd, intl, iberty and z library
• fix drkonqi compile issue (missing functions setenv/unsetenv) by adding kdewin
• fix include filename case issues on cross compiling
• fix missing includes

BUG:396821
FIXED-IN:5.13.5

Reviewed By: mlaurent
Differential Revision: https://phabricator.kde.org/D14423