tools/docs: sphinx-build-wrapper: move rust doc builder to wrapper

tools/docs: sphinx-build-wrapper: move rust doc builder to wrapper

Simplify even further the docs Makefile by moving rust build logic
to the wrapper.

After this change, running make on an environment with rust enabled
works as expected.

With CONFIG_RUST:

    $ make O=/tmp/foo LLVM=1 SPHINXDIRS=peci htmldocs
    make[1]: Entrando no diretório '/tmp/foo'

    Using alabaster theme
    Using Python kernel-doc
      GEN     Makefile
      DESCEND objtool
      CC      arch/x86/kernel/asm-offsets.s
      INSTALL libsubcmd_headers
      CALL    /new_devel/docs/scripts/checksyscalls.sh
      RUSTC L rust/core.o
      BINDGEN rust/bindings/bindings_generated.rs
      BINDGEN rust/bindings/bindings_helpers_generated.rs
    ...

Without it:
    $ make SPHINXDIRS=peci htmldocs
    Using alabaster theme
    Using Python kernel-doc

Both work as it is it is supposed to do.

After the change, it is also possible to build directly with the script
by passing "--rustodoc".

if CONFIG_RUST, this works fine:

    $ ./tools/docs/sphinx-build-wrapper --sphinxdirs peci --rustdoc -- htmldocs
    Using alabaster theme
    Using Python kernel-doc
      SYNC    include/config/auto.conf
    ...
      RUSTC L rust/core.o
    ...

If not, it will produce a warning that RUST may be disabled:

    $ ./tools/docs/sphinx-build-wrapper --sphinxdirs peci --rustdoc -- htmldocs
    Using alabaster theme
    Using Python kernel-doc
    ***
    *** Configuration file ".config" not found!
    ***
    *** Please run some configurator (e.g. "make oldconfig" or
    *** "make menuconfig" or "make xconfig").
    ***
    make[1]: *** [/new_devel/docs/Makefile:829: .config] Error 1
    make: *** [Makefile:248: __sub-make] Error 2
    Ignored errors when building rustdoc: Command '['make', 'LLVM=1', 'rustdoc']' returned non-zero exit status 2.. Is RUST enabled?

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Message-ID: <fa1235ccf859f6ebfeef7ffba0ebde2015a75042.1758196090.git.mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>