kconfig: use memcmp instead of deprecated bcmp

bcmp() was removed in POSIX.1-2008.

This commit replaces bcmp() with memcmp(). This allows Kconfig to link
with C libraries that do not provide bcmp(), such as Android bionic
libc.

Signed-off-by: Thomas Meyer <thomas@m3y3r.de>
Reviewed-by: Miguel Ojeda <ojeda@kernel.org>
Reported-by: Abhigyan Ghosh <zscript.team.zs@gmail.com>
[masahiro: update commit description]
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>