Rename some macros based on the PR review comments.

- use  the SWIFT prefix for all macros
- make names of some macros shorter

stdlib/public/runtime/Casting.cpp

@@ -498,11 +498,11 @@ _dynamicCastClassMetatype(const ClassMetadata *sourceType,
 }
 
 /// Dynamically cast a class instance to a Swift class type.
-RT_ENTRY_VISIBILITY
+SWIFT_RT_ENTRY_VISIBILITY
 const void *
 swift::swift_dynamicCastClass(const void *object,
                               const ClassMetadata *targetType)
-    CALLING_CONVENTION(RegisterPreservingCC_IMPL) {
+    SWIFT_CC(RegisterPreservingCC_IMPL) {
 #if SWIFT_OBJC_INTEROP
   assert(!targetType->isPureObjC());
 
@@ -2046,13 +2046,13 @@ checkDynamicCastFromOptional(OpaqueValue *dest,
 }
 
 /// Perform a dynamic cast to an arbitrary type.
-RT_ENTRY_VISIBILITY
+SWIFT_RT_ENTRY_VISIBILITY
 bool swift::swift_dynamicCast(OpaqueValue *dest,
                               OpaqueValue *src,
                               const Metadata *srcType,
                               const Metadata *targetType,
                               DynamicCastFlags flags)
-    CALLING_CONVENTION(RegisterPreservingCC_IMPL) {
+    SWIFT_CC(RegisterPreservingCC_IMPL) {
   auto unwrapResult = checkDynamicCastFromOptional(dest, src, srcType,
                                                    targetType, flags);
   srcType = unwrapResult.payloadType;