Split building of .o file from executable

[WardBrian]

Submisison Checklist

• Run tests: ./runCmdStanTests.py src/test
• Declare copyright holder and open-source license: see below

Summary:

Splits the make rule to build executables into two parts. This allows a more natural way to encode #1186, but also allows things like make mymodel.o, which would allow the same sort of thing and speed ups like stan-dev/stanc3#1350

Intended Effect:

How to Verify:

Side Effects:

None

Documentation:

Copyright and Licensing

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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/)

[andrjohns]

LGTM, thanks!

[WardBrian]

Question for the cmdstanr guys: is KEEP_OBJECT even needed with this, or can you just call make twice (make model.o, make model) to get to where you want?

[andrjohns]

Question for the cmdstanr guys: is KEEP_OBJECT even needed with this, or can you just call make twice (make model.o, make model) to get to where you want?

Mostly it would be nice so that we don't need to change any of the existing code for compiling models. But as you mention it's only a single additional call, so it's not essential