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 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.
 - 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