update target feature following LLVM API change

LLVM commit e817966718
renamed the `unaligned-scalar-mem` target feature to `fast-unaligned-access`.

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -263,6 +263,10 @@ pub fn to_llvm_features<'a>(sess: &Session, s: &'a str) -> LLVMFeature<'a> {
             "sve2-bitperm",
             TargetFeatureFoldStrength::EnableOnly("neon"),
         ),
+        // The unaligned-scalar-mem feature was renamed to fast-unaligned-access.
+        ("riscv32" | "riscv64", "fast-unaligned-access") if get_version().0 <= 17 => {
+            LLVMFeature::new("unaligned-scalar-mem")
+        }
         (_, s) => LLVMFeature::new(s),
     }
 }

compiler/rustc_codegen_ssa/src/target_features.rs

@@ -291,9 +291,9 @@ const RISCV_ALLOWED_FEATURES: &[(&str, Stability)] = &[
     ("d", Unstable(sym::riscv_target_feature)),
     ("e", Unstable(sym::riscv_target_feature)),
     ("f", Unstable(sym::riscv_target_feature)),
+    ("fast-unaligned-access", Unstable(sym::riscv_target_feature)),
     ("m", Stable),
     ("relax", Unstable(sym::riscv_target_feature)),
-    ("unaligned-scalar-mem", Unstable(sym::riscv_target_feature)),
     ("v", Unstable(sym::riscv_target_feature)),
     ("zba", Stable),
     ("zbb", Stable),

tests/ui/abi/riscv-discoverability-guidance.rs

@@ -2,9 +2,9 @@
 // revisions: riscv32 riscv64
 //
 // [riscv32] needs-llvm-components: riscv
-// [riscv32] compile-flags: --target=riscv32i-unknown-none-elf -C target-feature=-unaligned-scalar-mem --crate-type=rlib
+// [riscv32] compile-flags: --target=riscv32i-unknown-none-elf -C target-feature=-fast-unaligned-access --crate-type=rlib
 // [riscv64] needs-llvm-components: riscv
-// [riscv64] compile-flags: --target=riscv64gc-unknown-none-elf -C target-feature=-unaligned-scalar-mem --crate-type=rlib
+// [riscv64] compile-flags: --target=riscv64gc-unknown-none-elf -C target-feature=-fast-unaligned-access --crate-type=rlib
 #![no_core]
 #![feature(
     no_core,