Out of kernel kconfig patches rebased on 5.15

[Boris Kolpackov]

If anyone is interested in the kconfig functionality outside of the
kernel, I've rebased my portability patches on 5.15-rc7:

https://github.com/build2-packaging/kconfig/tree/upstream-5.15-rc7

There is also the liblkc library and conf/qconf configurators based
on this (similar to the now abandoned kconfig-frontends project):

https://github.com/build2-packaging/kconfig

Masahiro, if you like any of the patches, let me know and I will
send them for upsteaming (I don't want to make extra noise trying
all of them since most are probably not welcome):

https://github.com/build2-packaging/kconfig/commits/upstream-5.15-rc7