kbuild: Show marked Kconfig fragments in "help"

Currently the Kconfig fragments in kernel/configs and arch/*/configs
that aren't used internally aren't discoverable through "make help",
which consists of hard-coded lists of config fragments. Instead, list
all the fragment targets that have a "# Help: " comment prefix so the
targets can be generated dynamically.

Add logic to the Makefile to search for and display the fragment and
comment. Add comments to fragments that are intended to be direct targets.

Signed-off-by: Kees Cook <keescook@chromium.org>
Co-developed-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Kbuild: add Rust support

Having most of the new files in place, we now enable Rust support
in the build system, including `Kconfig` entries related to Rust,
the Rust configuration printer and a few other bits.

Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Co-developed-by: Alex Gaynor <alex.gaynor@gmail.com>
Signed-off-by: Alex Gaynor <alex.gaynor@gmail.com>
Co-developed-by: Finn Behrens <me@kloenk.de>
Signed-off-by: Finn Behrens <me@kloenk.de>
Co-developed-by: Adam Bratschi-Kaye <ark.email@gmail.com>
Signed-off-by: Adam Bratschi-Kaye <ark.email@gmail.com>
Co-developed-by: Wedson Almeida Filho <wedsonaf@google.com>
Signed-off-by: Wedson Almeida Filho <wedsonaf@google.com>
Co-developed-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Co-developed-by: Sven Van Asbroeck <thesven73@gmail.com>
Signed-off-by: Sven Van Asbroeck <thesven73@gmail.com>
Co-developed-by: Gary Guo <gary@garyguo.net>
Signed-off-by: Gary Guo <gary@garyguo.net>
Co-developed-by: Boris-Chengbiao Zhou <bobo1239@web.de>
Signed-off-by: Boris-Chengbiao Zhou <bobo1239@web.de>
Co-developed-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Co-developed-by: Douglas Su <d0u9.su@outlook.com>
Signed-off-by: Douglas Su <d0u9.su@outlook.com>
Co-developed-by: Dariusz Sosnowski <dsosnowski@dsosnowski.pl>
Signed-off-by: Dariusz Sosnowski <dsosnowski@dsosnowski.pl>
Co-developed-by: Antonio Terceiro <antonio.terceiro@linaro.org>
Signed-off-by: Antonio Terceiro <antonio.terceiro@linaro.org>
Co-developed-by: Daniel Xu <dxu@dxuuu.xyz>
Signed-off-by: Daniel Xu <dxu@dxuuu.xyz>
Co-developed-by: Björn Roy Baron <bjorn3_gh@protonmail.com>
Signed-off-by: Björn Roy Baron <bjorn3_gh@protonmail.com>
Co-developed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Signed-off-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>