Add __printflike attribution to use vprintf and friends with an argument
as format string.

Split out the -lpthread tests to a separate file.

XXX: The only thing gained from this is seeing whether -lpthread breaks
the getenv(3) family. Yet, a strict hypothesis about this would require

Split out the -lpthread tests to a separate file.

XXX: The only thing gained from this is seeing whether -lpthread breaks
the getenv(3) family. Yet, a strict hypothesis about this would require
that the two test files are identical, which they are not.

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