[C++][Dataset] regex_error in hive partition on centos7 and opensuse42

[asfimport]

See https://github.com/apache/arrow/runs/373769666#step:5:3301 and https://github.com/apache/arrow/runs/373769676#step:5:3297:

 ```Java

══ Failed ══════════════════════════════════════════════════════════════════════
── 1. Error: Hive partitioning (@test-dataset.R#89) ───────────────────────────
regex_error
Backtrace:

1. arrow::open_dataset(...) testthat/test-dataset.R:89:2
2. dsd$Finish(schema)
3. arrow:::dataset___DSDiscovery__Finish2(self, schema)

 

**Reporter**: [Neal Richardson](https://issues.apache.org/jira/browse/ARROW-7500) / @nealrichardson
**Assignee**: [Ben Kietzman](https://issues.apache.org/jira/browse/ARROW-7500) / @bkietz
#### PRs and other links:
- [GitHub Pull Request #6137](https://github.com/apache/arrow/pull/6137)

<sub>**Note**: *This issue was originally created as [ARROW-7500](https://issues.apache.org/jira/browse/ARROW-7500). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*</sub>

[asfimport]

Neal Richardson / @nealrichardson:
Related to ARROW-6445?

[asfimport]

Ben Kietzman / @bkietz:
@nealrichardson Probably, since the failing builds in both ARROW-6445 and this issue include older GCC standard libraries. I'm not sure why the build didn't just fail (instead we have a runtime error) but in any case I'll try removing the std::regex usage and see if that resolves it

[asfimport]

Neal Richardson / @nealrichardson:
Issue resolved by pull request 6137
#6137