[clang] [FMV] Emit the resolver along with the default version definition. (PR #84405)

[Jon Roelofs via cfe-commits]

jroelofs wrote:

I'm referring to:
```
  // This should generate a normal function.
  int __attribute__((target_version("rdm"))) unused_without_default(void);
```

and:
```
  // CHECK: Function Attrs: noinline nounwind optnone
+ // CHECK-LABEL: define {{[^@]+}}@unused_without_default
+ // CHECK-SAME: () #[[ATTR17:[0-9]+]] {
  // CHECK-NEXT:  entry:
+ // CHECK-NEXT:    ret i32 0
 ```
 
 and am confused why `int __attribute__((target_version("rdm"))) unused_without_default(void)`'s mangling will be `_ unused_without_default` and not `_unused_without_default._Mrdm`.

https://github.com/llvm/llvm-project/pull/84405