[orc-rt] Add unit test for "re-throwing" errors in handleErrors. (#178112)

handleErrors supports several different handler signatures, including
handlers that take a unique_ptr<T> (where T is a descendant of
ErrorInfoBase) and return an Error: (std::unique_ptr<T>) -> Error. In
this case the handler should be able to create an Error value to wrap
the original ErrorInfoBase object without.

This functionality was not previously tested, and will be used in
upcoming commits. This commit adds the missing test coverage.

orc-rt/unittests/ErrorTest.cpp

@@ -284,6 +284,21 @@ TEST(ErrorTest, IsAHandling) {
   consumeError(std::move(G));
 }
 
+TEST(Error, ReReturnErrorFromHandler) {
+  int ErrorInfo = 0;
+
+  Error E = handleErrors(make_error<CustomError>(7),
+                         [&](std::unique_ptr<CustomError> CE) {
+                           return make_error(std::move(CE));
+                         });
+
+  handleAllErrors(std::move(E),
+                  [&](const CustomError &CE) { ErrorInfo = CE.getInfo(); });
+
+  EXPECT_EQ(ErrorInfo, 7)
+      << "Failed to handle Error returned from handleErrors.";
+}
+
 TEST(ErrorTest, StringError) {
   auto E = make_error<StringError>("foo");
   if (E.isA<StringError>())