rust: x86: support Rust >= 1.98.0 target spec

Starting with Rust 1.98.0 (expected 2026-08-20), the target spec will not
support `x86-softfloat` anymore [1]. Instead, `softfloat` should be used.

Thus conditionally use one or the other depending on the version.

The alias has been there since Rust 1.95.0 (released 2026-04-16).

Cc: Ralf Jung <post@ralfj.de>
Cc: Alice Ryhl <aliceryhl@google.com>
Link: rust-lang/rust#157151 [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

scripts/generate_rust_target.rs

@@ -196,7 +196,9 @@ fn main() {
         }
     } else if cfg.has("X86_64") {
         ts.push("arch", "x86_64");
-        if cfg.rustc_version_atleast(1, 86, 0) {
+        if cfg.rustc_version_atleast(1, 98, 0) {
+            ts.push("rustc-abi", "softfloat");
+        } else if cfg.rustc_version_atleast(1, 86, 0) {
             ts.push("rustc-abi", "x86-softfloat");
         }
         ts.push(