config.cache is not generated or used on my Windows installation of MinGW unless --config-cache is also given as argument to configure, and from the autoconf documentation this seems to be the default behaviour.  So you might want to amend the instructions to take that into account.

Isn't requiring the user to manually create and edit config.cache resulting in unnecessary work and confusion for the them when it can be addressed in configure.in?  Given that checking files is an operation which does not work when cross_compiling is set and checking them results in configure exiting because of this, configure.in can check cross_compiling before trying these checks and avoid them allowing configure to complete.