prereq-build: require python3-distutils

prereq-build: require python3-distutils

Debian and Ubuntu ship a python3-minimal package which does not include
the distutils module. This is not supported by upstream and can be
considered a broken python distribution.

In practice, many scripts depend on said module, and this is a reoccuring
pain point for building various OpenWrt packages.

Require and check for said module, enough time has been wasted on this.

A list of just the most recent issues:
https://github.com/openwrt/packages/pull/16304
https://github.com/openwrt/packages/pull/16027
https://github.com/openwrt/packages/pull/15443
https://github.com/openwrt/packages/pull/14394
https://github.com/openwrt/packages/pull/12909
https://github.com/openwrt/packages/issues/12443
https://github.com/openwrt/packages/pull/11035
https://github.com/openwrt/packages/issues/10993

Signed-off-by: Andre Heider <a.heider@gmail.com>