ABI checks: add support for loongarch

LoongArch psABI[^1] specifies that LSX vector types are passed via general-purpose
registers, while LASX vector types are passed indirectly through the stack.
This patch addresses the following warnings:
```
warning: this function call uses a SIMD vector type that is not currently supported with the chosen ABI
--> .../library/core/src/../../stdarch/crates/core_arch/src/loongarch64/lsx/generated.rs:3695:5
|
3695 | __lsx_vreplgr2vr_b(a)
| ^^^^^^^^^^^^^^^^^^^^^ function called here
|
= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
= note: for more information, see issue #116558 <#116558>
= note: `#[warn(abi_unsupported_vector_types)]` on by default
```
[^1]: https://github.com/loongson/la-abi-specs/blob/release/lapcs.adoc

Author: heiher

compiler/rustc_target/src/target_features.rs

@@ -611,6 +611,8 @@ const HEXAGON_FEATURES_FOR_CORRECT_VECTOR_ABI: &'static [(u64, &'static str)] =
 &[/*(512, "hvx-length64b"),*/(1024,"hvx-length128b")];
 constMIPS_FEATURES_FOR_CORRECT_VECTOR_ABI:&'static[(u64,&'staticstr)] = &[(128,"msa")];
 constCSKY_FEATURES_FOR_CORRECT_VECTOR_ABI:&'static[(u64,&'staticstr)] = &[(128,"vdspv1")];
+constLOONGARCH_FEATURES_FOR_CORRECT_VECTOR_ABI:&'static[(u64,&'staticstr)] =
+&[(128,"lsx"),(256,"lasx")];
 
 implsuper::spec::Target{
 pubfnrust_target_features(&self) -> &'static[(&'staticstr,Stability,ImpliedFeatures)]{
@@ -638,7 +640,7 @@ impl super::spec::Target {
 "aarch64" | "arm64ec" => AARCH64_FEATURES_FOR_CORRECT_VECTOR_ABI,
 "arm" => ARM_FEATURES_FOR_CORRECT_VECTOR_ABI,
 "powerpc" | "powerpc64" => POWERPC_FEATURES_FOR_CORRECT_VECTOR_ABI,
-"loongarch64" => &[],// on-stack ABI, so we complain about all by-val vectors
+"loongarch64" => LOONGARCH_FEATURES_FOR_CORRECT_VECTOR_ABI,
 "riscv32" | "riscv64" => RISCV_FEATURES_FOR_CORRECT_VECTOR_ABI,
 "wasm32" | "wasm64" => WASM_FEATURES_FOR_CORRECT_VECTOR_ABI,
 "s390x" => S390X_FEATURES_FOR_CORRECT_VECTOR_ABI,