> Well, it is important to somehow get the build information for
> Python, since that tells us which OS features were available
> at the time of compilation.

No, it doesn't (except for a bug that Matthias Klose pointed out).
The OS kernel version should have *zero* impact on the resulting Python
binary. What matters it the C compiler and the version of the C library.
The C library may or may not have features; features of the kernel used
to build Python are completely irrelevant.

(I think you misunderstood an earlier statement of me as
self-contradicting. It was not: The kernel *headers* may have an
impact during autoconf, not the running kernel. For Linux, the
kernel headers are part of the C library, and typically bear no
relationship with the running kernel - i.e. they may be either older
or newer than the running kernel).

Since there is no chance that we get the build environment captured
in a reasonable way (in particular not the version of the C library,
in a cross-platform manner), I strongly recommend to let this aspect
rest.