rust: make mutually exclusive with CFI_CLANG

On RISC-V and arm64, and presumably x86, if CFI_CLANG is enabled,
loading a rust module will trigger a kernel panic. Support for
sanitisers, including kcfi (CFI_CLANG), is in the works, but for now
they're nightly-only options in rustc. Make RUST depend on !CFI_CLANG
to prevent configuring a kernel without symmetrical support for kfi.

[ Matthew Maurer writes [1]:

This patch is fine by me - the last patch needed for KCFI to be
functional in Rust just landed upstream last night, so we should
revisit this (in the form of enabling it) once we move to
`rustc-1.79.0` or later.

Ramon de C Valle also gave feedback [2] on the status of KCFI for
Rust and created a tracking issue [3] in upstream Rust. - Miguel ]

Fixes: 2f7ab1267dc9 ("Kbuild: add Rust support")
Cc: [e-mail]
Signed-off-by: Conor Dooley <[e-mail]>
Acked-by: Nathan Chancellor <[e-mail]>
Link: https://lore.kernel.org/rust-for-linux/[e-mail]/ [1]
Link: https://lore.kernel.org/rust-for-linux/CAOcBZOS2kPyH0Dm7Fuh4GC3=[e-mail]/ [2]
Link: https://github.com/rust-lang/rust/issues/123479 [3]
Link: https://lore.kernel.org/r/20240404-providing-emporium-e652e359c711@spud
[ Added feedback from the list, links, and used Cc for the tag. ]
Signed-off-by: Miguel Ojeda <[e-mail]>

init/Kconfig

···
 	bool "Rust support"
 	depends on HAVE_RUST
 	depends on RUST_IS_AVAILABLE
+	depends on !CFI_CLANG
 	depends on !MODVERSIONS
 	depends on !GCC_PLUGINS
 	depends on !RANDSTRUCT