rustc_codegen_llvm: Split "Fixed in LLVM 20" cases

... in `update_target_reliable_float_cfg`, based on the actual changes.
The AArch64 issue is fixed on LLVM 20.1.1 while the MIPS issue is fixed
on LLVM 20.1.0 (the first LLVM 20 release).

This commit distinguishes two separate cases.

Author: a4lg

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -335,11 +335,12 @@ fn update_target_reliable_float_cfg(sess: &Session, cfg: &mut TargetConfig) {
     let target_abi = sess.target.options.abi.as_ref();
     let target_pointer_width = sess.target.pointer_width;
     let version = get_version();
+    let lt_20_1_0 = version < (20, 1, 0);
     let lt_20_1_1 = version < (20, 1, 1);
     let lt_21_0_0 = version < (21, 0, 0);
 
     cfg.has_reliable_f16 = match (target_arch, target_os) {
-        // LLVM crash without neon <https://github.com/llvm/llvm-project/issues/129394> (fixed in llvm20)
+        // LLVM crash without neon <https://github.com/llvm/llvm-project/issues/129394> (fixed in LLVM 20.1.1)
         ("aarch64", _)
             if !cfg.target_features.iter().any(|f| f.as_str() == "neon") && lt_20_1_1 =>
         {
@@ -367,7 +368,7 @@ fn update_target_reliable_float_cfg(sess: &Session, cfg: &mut TargetConfig) {
         // Unsupported <https://github.com/llvm/llvm-project/issues/94434>
         ("arm64ec", _) => false,
         // Selection bug <https://github.com/llvm/llvm-project/issues/96432> (fixed in llvm20)
-        ("mips64" | "mips64r6", _) if lt_20_1_1 => false,
+        ("mips64" | "mips64r6", _) if lt_20_1_0 => false,
         // Selection bug <https://github.com/llvm/llvm-project/issues/95471>. This issue is closed
         // but basic math still does not work.
         ("nvptx64", _) => false,