build-infra: Freetype error message is confusing

If we don't find freetype on Windows, we print:
configure: error: Could not find libfreetype.se nor freetype.dll in /usr/X11R6/lib

This is confusing since we did'nt expect to find it there on Windows. We've had at least one bug report where the reporter were confused by this.

We should adapt the error message to be more appropriate about what we have actually checked and/or what we expected to find.