Fix further int-size ambiguities

[andrjohns]

Submission Checklist

• Run unit tests: ./runTests.py src/test/unit
• Run cpplint: make cpplint
• Declare copyright holder and open-source license: see below

Summary

Follow-up fix to #3406, the uint64_t typedef can be inconsistent between platforms (e.g., unsigned long vs unsigned long long) which breaks some of the overload resolution in the stan writer, so this just adds the separate overloads to fix support across all

Intended Effect

Fix compilation under macos

How to Verify

Side Effects

Documentation

Fixed compilation errors under MacOS due to ambiguous int typedefs

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company): Andrew Johnson

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)