ORC-480: [C++] Add an option to succeed despite warnings
ORC-480: [C++] Add an option to succeed despite warnings

The extensive warnings that are set are useful for CI and development,
but a nuisance for external packagers and dependent projects which
can encounter failing builds because of warnings in ORC.

Fixes #441

Signed-off-by: Owen O'Malley <54ea18af6a9d2f71f251392755b45ef039a9facd@apache.org>

omalley/orc,apache/orc,omalley/orc,apache/orc,apache/orc,apache/orc,omalley/orc,apache/orc,omalley/orc,apache/orc,apache/orc,omalley/orc,omalley/orc,omalley/orc,apache/orc