[clang] [clang][LoongArch] Ensure `target("lasx")` implies LSX support (PR #153542)

[Lu Weining via cfe-commits]

================
@@ -460,7 +460,12 @@ LoongArchTargetInfo::parseTargetAttr(StringRef Features) const {
       break;
 
     case AttrFeatureKind::Feature:
-      Ret.Features.push_back("+" + Value.str());
+      if (Value == "lasx") {
+        Ret.Features.push_back("+lasx");
+        Ret.Features.push_back("+lsx");
+      } else {
+        Ret.Features.push_back("+" + Value.str());
+      }
----------------
SixWeining wrote:

```suggestion
      Ret.Features.push_back("+" + Value.str());
      if (Value == "lasx")
        Ret.Features.push_back("+lsx");
```

https://github.com/llvm/llvm-project/pull/153542