Porting: gammafunction: Add constants for ieeeQuadruple reals

[jpf91]

Setting MAXGAMMA to the same as for ieeeExtended reals means the range of the gamma function will be limited to the same range as ieeeExtended. However, until someone reviews the algorithm to work fine for ieeeQuadruple ranges, this workaround seems fine. We just lose some 128bit real features, but we're still as good as x86.

This is a revival of #4047

[dlang-bot]

Thanks for your pull request, @jpf91! We are looking forward to reviewing it, and you should be hearing from a maintainer soon.

Some tips to help speed things up:

• smaller, focused PRs are easier to review than big ones

• try not to mix up refactoring or style changes with bug fixes or feature enhancements

• provide helpful commit messages explaining the rationale behind each change

Bear in mind that large or tricky changes may require multiple rounds of review and revision.

Please see CONTRIBUTING.md for more information.

Bugzilla references

Your PR doesn't reference any Bugzilla issue.

If your PR contains non-trivial changes, please reference a Bugzilla issue or create a manual changelog.

[andralex]

not an expert but lgtm

[jpf91]

Thanks!