[clang] [AArch64] Add MSVC mangling for the __mfp8 type (PR #124968)

[Benjamin Maxwell via cfe-commits]

================
@@ -2808,6 +2812,7 @@ void MicrosoftCXXNameMangler::mangleType(const BuiltinType *T, Qualifiers,
 
 #define SVE_TYPE(Name, Id, SingletonId) \
   case BuiltinType::Id:
+#define SVE_SCALAR_TYPE(Name, MangledName, Id, SingletonId, Bits)
----------------
MacDue wrote:

Is there a reason why this can't be handled by defining `SVE_SCALAR_TYPE` to the the mangling? 
I was a little confused about what this empty define was doing at first.

```suggestion
#define SVE_SCALAR_TYPE(Name, MangledName, Id, SingletonId, Bits)  \
    mangleArtificialTagType(TagTypeKind::Struct, MangledName);     \
    break;
```
Also, is there anyone we can tag that knows about the Microsoft mangling? I'm not sure if there's any process needed for adding a new type.

https://github.com/llvm/llvm-project/pull/124968