[Object] Change Archive::child_iterator for better interop with Error/Expected.

See http://reviews.llvm.org/D22079

Changes the Archive::child_begin and Archive::children to require a reference
to an Error. If iterator increment fails (because the archive header is
damaged) the iterator will be set to 'end()', and the error stored in the
given Error&. The Error value should be checked by the user immediately after
the loop. E.g.:

Error Err;
for (auto &C : A->children(Err)) {
  // Do something with archive child C.
}
// Check the error immediately after the loop.
if (Err)
  return Err;

Failure to check the Error will result in an abort() when the Error goes out of
scope (as guaranteed by the Error class).



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@275316 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Support/Error.cpp

@@ -64,6 +64,7 @@ void logAllUnhandledErrors(Error E, raw_ostream &OS, Twine ErrorBanner) {
   });
 }
 
+
 std::error_code ErrorList::convertToErrorCode() const {
   return std::error_code(static_cast<int>(ErrorErrorCode::MultipleErrors),
                          *ErrorErrorCat);
@@ -99,4 +100,14 @@ std::error_code StringError::convertToErrorCode() const {
   return EC;
 }
 
+void report_fatal_error(Error Err, bool GenCrashDiag) {
+  assert(Err && "report_fatal_error called with success value");
+  std::string ErrMsg;
+  {
+    raw_string_ostream ErrStream(ErrMsg);
+    logAllUnhandledErrors(std::move(Err), ErrStream, "");
+  }
+  report_fatal_error(ErrMsg);
+}
+
 }