x86: rust: move unknown-to-rustc codegen features back to the targe…

…t spec file

Only a subset of the LLVM codegen features are recognized by `rustc`,
and since rust-lang/rust#87402 (Rust 1.61.0)
the compiler gives a warning about it:

    warning: unknown feature specified for `-Ctarget-feature`: `mmx`
      |
      = note: it is still passed through to the codegen backend
      = note: consider filing a feature request

...since those features may be renamed or removed at any point:

    $ rustc --print target-features

    [...]

    Code-generation features cannot be used in cfg or #[target_feature],
    and may be renamed or removed in a future version of LLVM or rustc.

Thus move them back to the target spec generated file.

See rust-lang/rust#96472 as well for a report.

Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

arch/x86/Makefile

@@ -63,8 +63,7 @@ export BITS
 #    https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
 #
 KBUILD_CFLAGS += -mno-sse -mno-mmx -mno-sse2 -mno-3dnow -mno-avx
-KBUILD_RUSTFLAGS += -Ctarget-feature=-mmx,-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2
-KBUILD_RUSTFLAGS += -Ctarget-feature=-3dnow,-3dnowa,-avx,-avx2,+soft-float
+KBUILD_RUSTFLAGS += -Ctarget-feature=-sse,-sse2,-sse3,-ssse3,-sse4.1,-sse4.2,-avx,-avx2
 
 ifeq ($(CONFIG_X86_KERNEL_IBT),y)
 #

scripts/generate_rust_target.rs

@@ -204,6 +204,7 @@ fn main() {
             "data-layout",
             "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128",
         );
+        ts.push("features", "-3dnow,-3dnowa,-mmx,+soft-float");
         ts.push("llvm-target", "x86_64-linux-gnu");
         ts.push("target-pointer-width", "64");
     } else {