These files were taken from the Linux Kernel Configuration System at commit
089b7d890f972f6b649fedc9259f6b93a18fb970 (Feb 4, 2020) and modified for the
OpenWrt Buildroot:
 - Removed nconf, gconf, tests and kernel configuration targets.
 - Adjusted the Makefile to compile outside the kernel.
 - Always use default file when running make all{no,mod,yes}config.
 - Added a 'reset' command to reset config when the target changes.
 - Allow config reading from & writing to a different file.
 - Allow 'source' command to use globs to include multiple files.
 - Don't warn when selecting a symbol with unmet direct dependencies.
 - Don't write auto.conf and other files under include/ directory.
 - Reverted a commit to allow use of '/' & '.' in unquoted config symbols.
   There are too many of those in OpenWrt right now.
 - Reverted a commit that was issuing a warning when there were more than
   one help text.  This is used in a few packages to use different texts
   for the menuconfig help, and the ipkg package description.
 - Reverted an upstream change that avoids writing symbols that are not
   visible to .config, which breaks OpenWrt busybox's '.config' generation
   logic.
 - Treat recursive dependency as a warning only; add a --fatalrecursive
   option to conf to treat recursive deps as a fatal error.
 - Use pre-built *.lex.c *.tab.[ch] files by default, to avoid depending on
   flex & bison.  Rebuild/remove these files only if running make with
   BUILD_SHIPPED_FILES defined

For a full list of changes, see the repository at:
https://github.com/cotequeiroz/linux/commits/openwrt/scripts/kconfig