Use platform tag from sysconfig.platform on non-portable Linux

[messense]

Stop hard-code linux platform tag for non-portable Linux. This allows build linux_armv8l wheels on 64-bit Linux running in 32-bit mode, for example linux32 python3 -m sysconfig:

Platform: "linux-armv8l"
Python version: "3.8"
Current installation scheme: "posix_prefix"

This removes the need for patch on Alpine Linux armhf and armv7 CI runners, it was painful.

I've tested on a Raspberry Pi running a 64-bit Ubuntu.

See also pypa/packaging#476

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[messense]

Still having issue with abi3 since it doesn't use a Python interpreter on Linux.

Fixed in d5c8f6d