[Runtime] Add a function pointer for intercepting swift_willThrow calls.

rdar://problem/53400364

stdlib/public/runtime/ErrorObjectNative.cpp

@@ -106,11 +106,4 @@ swift::swift_getErrorValue(const SwiftError *errorObject,
   out->errorConformance = errorObject->errorConformance;
 }
 
-/// Breakpoint hook for debuggers.
-SWIFT_CC(swift) void
-swift::swift_willThrow(SWIFT_CONTEXT void *unused,
-                       SWIFT_ERROR_RESULT SwiftError **error) {
-  // do nothing
-}
-
 #endif