Update unpack_template.h
- [x ] closes #14373
- [ ] tests added / passed
- [ ] passes `git diff upstream/master | flake8 --diff`
- [ ] whatsnew entry

USE_CASE_RANGE is a GNU C feature. This change will activate
USE_CASE_RANGE on any platform when using GNU C and not on any platform
when a different compiler is being used.

closes #14373

## [Current coverage](https://codecov.io/gh/pandas-dev/pandas/pull/14441?src=pr) is 85.25% (diff: 100%)

> Merging [#14441](https://codecov.io/gh/pandas-dev/pandas/pull/14441?src=pr) into [master](https://codecov.io/gh/pandas-dev/pandas/branch/master?src=pr) will decrease coverage by **<.01%**

``` diff
@@             master     #14441   diff @@
==========================================
  Files           140        140          
  Lines         50631      50631          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
- Hits          43167      43166     -1   
- Misses         7464       7465     +1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [7cad3f1...1824bad](https://codecov.io/gh/pandas-dev/pandas/compare/7cad3f16bccd1d4702ef9d038b1ee0db33b9bb94...1824bad1d7a67b4efa318f207f98bb88ea3368eb?src=pr)
 can you push this again. since we changed the url of the repo, I think appveyor got turned off. I just turned it back on.

you can do:

`git commit --all --amend -C HEAD`  generate a revised hash
`git push yourbranchname yourrepo -f` to force the update
 rebuilding server after a NAS crash - will do later tomorrow.
 thanks @aixtools this builds.
