Generate a header containing the private QDLDL config options

[imciner2]

This is the first half of a fix to make the qdldl-python package work. Basically, that package needs access to the DLONG define that the QDLDL sources use for defining their integer types, so this commit writes out that information into a standalone configure header (similar to the way it is done in OSQP).

[coveralls]

Pull Request Test Coverage Report for Build 174

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 170:	0.0%
Covered Lines:	87
Relevant Lines:	87

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💛 - Coveralls

[coveralls]

Pull Request Test Coverage Report for Build 1290796522

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 1221906610:	0.0%
Covered Lines:	87
Relevant Lines:	87

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💛 - Coveralls

[bstellato]

Thanks for making that change. Just a minor comment, how about putting these new lines together with the qdldl_types.h.in file? I am not sure we need two separate files for doing something very closely related.

[imciner2]

Ok, I have changed this to write the two configuration defines into the existing qdldl_types.h header that we generate, and have also namespaced them into QDLDL_* so that we don't leak them into other applications (such as OSQP when we include the QDLDL headers).