By default AIX builds 32-bit applications - and the combined .data, .bss and .stack areas share one memory segment of 256 Mbyte.

This can be modified by either specifying a larger value for maxdata during linking (e.g., with LDFLAGS=-bmaxdata:0x40000000) or using the program ldedit (e.g., ldedit -b maxdata:0x40000000).

The subtest test_shutil.test_unpack_archive_xztar fails with the default. The patch here looks at the MAXDATA value of the executable XCOFF headers and skips the test when AIX is 32-bit and MAXDATA < 0x20000000.

This helps the result of AIX bots to be more accurate - as this so-called failure is not an issue with python itself.