[Runtime][ABI] Have swift_willThrow take the error value in the return register.

rdar://problem/37578477

stdlib/public/runtime/ErrorObjectNative.cpp

@@ -106,6 +106,11 @@ swift::swift_getErrorValue(const SwiftError *errorObject,
   out->errorConformance = errorObject->errorConformance;
 }
 
-void swift::swift_willThrow(SwiftError *object) { }
+/// Breakpoint hook for debuggers.
+SWIFT_CC(swift) void
+swift::swift_willThrow(SWIFT_CONTEXT void *unused,
+                       SWIFT_ERROR_RESULT SwiftError **error) {
+  // do nothing
+}
 
 #endif