Fix configure check for freetype version

Unfortunately the versions reported by system freetype packages with
pkg-config are not always consistent with the actual freetype version.

Instead, we now use a compile time check, similar to what the
corresponding check for qtgui does.

Change-Id: I3316f5dfe423ffead5fd9cfec1542407c2b21bd8
Fixes: QTBUG-71033
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>