rust: Disallow BTF generation with Rust + LTO

The kernel cannot currently self-parse BTF containing Rust debug
information. pahole uses the language of the CU to determine whether to
filter out debug information when generating the BTF. When LTO is
enabled, Rust code can cross CU boundaries, resulting in Rust debug
information in CUs labeled as C. This results in a system which cannot
parse its own BTF.

Signed-off-by: Matthew Maurer <mmaurer@google.com>
Cc: stable@vger.kernel.org
Fixes: c117797 ("btf, scripts: Exclude Rust CUs with pahole")
Link: https://lore.kernel.org/r/20250108-rust-btf-lto-incompat-v1-1-60243ff6d820@google.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: maurer

init/Kconfig

@@ -1973,7 +1973,7 @@ config RUST
 	depends on !MODVERSIONS || GENDWARFKSYMS
 	depends on !GCC_PLUGIN_RANDSTRUCT
 	depends on !RANDSTRUCT
-	depends on !DEBUG_INFO_BTF || PAHOLE_HAS_LANG_EXCLUDE
+	depends on !DEBUG_INFO_BTF || (PAHOLE_HAS_LANG_EXCLUDE && !LTO)
 	depends on !CFI_CLANG || HAVE_CFI_ICALL_NORMALIZE_INTEGERS_RUSTC
 	select CFI_ICALL_NORMALIZE_INTEGERS if CFI_CLANG
 	depends on !CALL_PADDING || RUSTC_VERSION >= 108100