We started using clang to emit the _OBJC_PROTOCOL_ definition.
But we would use a different name for the proto_list definition than clang.
"OBJC_LABEL_PROTOCOL$" (objc)
|--> OBJC_PROTOCOL
"\01l_OBJC_LABEL_PROTOCOL$_" (swift)
|--> OBJC_PROTOCOL
If an Objective C object also emitted the same protocol definition you could
end up in a situation where both clang's and swift's proto_list definitions
point to the same protocol definition.
Older linkers don't like that.
rdar://108505376
There are certain protocol method decls types that swift does not import
today.
```
@protocol Incomplete
- (id)getObjectFromVarArgs:(id)first, ...;
@end
```
Furthermore, the old method also emitted duplicate entries for protocols
methods when Swift synthesized methods for diagnosics.
We won't import this method into Swift. So if we emit protocol metadata
from swift delcs we would generate incomplete records.
rdar://60888524
