build: kern: support per-KERNCONF LOCAL_MODULES overrides

[kevans]

Summary

It may be the case that one wants to build multiple KERNCONFs in one
buildkernel with some different LOCAL_MODULES options; e.g., build
machine configs likely don't need drm-kmod from ports.

This lets us configure LOCAL_MODULES_DIR_${KERNCONF} and/or
LOCAL_MODULES_${KERNCONF} as needed to override whatever global defaults
may be supplied.

[dan.mcgregor_usask.ca]

Thank you so much for this. I thought of doing it myself.

[jhb]

Did you try setting LOCAL_MODULES or LOCAL_MODULES_DIR in a kernel config via makeoptions? You can set things like NO_MODULES=yes and MODULES_OVERRIDE in kernel config files via makeoptions.

[kevans]

In D28626#642816, @jhb wrote:

Did you try setting LOCAL_MODULES or LOCAL_MODULES_DIR in a kernel config via makeoptions? You can set things like NO_MODULES=yes and MODULES_OVERRIDE in kernel config files via makeoptions.

I was trying to avoid creating a custom config just for that; build machine runs GENERIC-NODEBUG while everything else runs GENERIC or MINIMAL.