Explicity disable LSX feature for loongarch64-unknown-none target

The `loongarch64-unknown-none` target is a bare-metal target with
hardware floating-point support and should not enable SIMD extensions
by default. However, LLVM's LoongArch64 backend enables LSX implicitly,
inadvertently activating SIMD instructions for this target. This patch
explicitly disable LSX feature to prevent unintended SIMD usage.

Author: heiher

compiler/rustc_target/src/spec/targets/loongarch64_unknown_none.rs

@@ -17,7 +17,7 @@ pub(crate) fn target() -> Target {
         arch: "loongarch64".into(),
         options: TargetOptions {
             cpu: "generic".into(),
-            features: "+f,+d".into(),
+            features: "+f,+d,-lsx".into(),
             linker_flavor: LinkerFlavor::Gnu(Cc::No, Lld::Yes),
             linker: Some("rust-lld".into()),
             llvm_abiname: "lp64d".into(),