Revert "[WASM] Sync calling convention between C++ and Swift"

This reverts commit 662d7bd.

Author: kateinoigakukun

include/swift/Runtime/HeapObject.h

@@ -137,7 +137,6 @@ HeapObject* swift_allocEmptyBox();
 /// It may also prove worthwhile to have this use a custom CC
 /// which preserves a larger set of registers.
 SWIFT_RUNTIME_EXPORT
-SWIFT_CC(swift)
 HeapObject *swift_retain(HeapObject *object);
 
 SWIFT_RUNTIME_EXPORT

include/swift/Runtime/RuntimeFunctions.def

@@ -182,7 +182,7 @@ FUNCTION(CopyPOD, swift_copyPOD, C_CC, AlwaysAvailable,
          EFFECT(NoEffect))
 
 // void *swift_retain(void *ptr);
-FUNCTION(NativeStrongRetain, swift_retain, SwiftCC, AlwaysAvailable,
+FUNCTION(NativeStrongRetain, swift_retain, C_CC, AlwaysAvailable,
          RETURNS(RefCountedPtrTy),
          ARGS(RefCountedPtrTy),
          ATTRS(NoUnwind, FirstParamReturned, WillReturn),

stdlib/public/runtime/HeapObject.cpp

@@ -354,7 +354,6 @@ static HeapObject *_swift_retain_(HeapObject *object) {
   return object;
 }
 
-SWIFT_CC(swift)
 HeapObject *swift::swift_retain(HeapObject *object) {
 #ifdef SWIFT_THREADING_NONE
   return swift_nonatomic_retain(object);