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At the time the code was written, libc and glibc were in wide spread use, so it's not surprising that it doesn't work well for other C libs.
Note that the routine returns the highest libc version number used and required by the executable (usually the Python interpreter). This does not necessarily correspond to the version installed on the system. The purpose of the function was to determine the minimum libc compatibility requirements of the executable.
The routine you quote uses ctypes and only works for glibc, so parsing needs to be kept around as fallback solution. It also returns the libc version that is currently used on the system; not necessarily the minimum version required, so semantics are different.