swift_allocError should use the Swift calling convention

Author: bryanpkc

stdlib/public/runtime/ErrorObject.cpp

@@ -62,6 +62,8 @@ static const FullMetadata<HeapMetadata> ErrorProtocolMetadata{
   Metadata{MetadataKind::ErrorObject},
 };
 
+SWIFT_CC(swift) SWIFT_RUNTIME_EXPORT
+extern "C"
 BoxPair::Return
 swift::swift_allocError(const swift::Metadata *type,
                         const swift::WitnessTable *errorConformance,

stdlib/public/runtime/ErrorObject.h

@@ -142,7 +142,7 @@ struct SwiftError : SwiftErrorHeader {
 /// copied (or taken if \c isTake is true) into the newly-allocated error box.
 /// If value is null, the box's contents will be left uninitialized, and
 /// \c isTake should be false.
-SWIFT_RUNTIME_EXPORT
+SWIFT_CC(swift) SWIFT_RUNTIME_EXPORT
 extern "C" BoxPair::Return swift_allocError(const Metadata *type,
                                           const WitnessTable *errorConformance,
                                           OpaqueValue *value, bool isTake);