ORC-815: Build and test C++ module on CLang12
ORC-815: Build and test C++ module on CLang12

This PR aims to build and test the C++ module on CLang12

Currently, the build fails with new warnings.

Manually built and tested.
```
$ make test-out
Test project /Users/william/orc/build
    Start 1: orc-test
1/2 Test #1: orc-test .........................   Passed    3.99 sec
    Start 2: tool-test
2/2 Test #2: tool-test ........................   Passed   11.96 sec

100% tests passed, 0 tests failed out of 2
```

Closes #718

Signed-off-by: William Hyun <c824fe0afe16857dd6f587aa7c4044d2642d60fb@apache.org>

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