fix(aix): add aix directory synchronization support

[pmur]

AIX doesn't support a proper flock like linux, but it seems to have enough support for process level file locking using fcntl.

For #2035

Problem

GOOS=aix does not build. AIX does not support a linux-like flock, and does not export unix.Flock.

Solution

Create an AIX specific directory-locking implementation using the AIX version of flock.

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[pmur]

Hi, is there something I need to fix in the CL, or is this a CI issue?

[github-actions]

This PR has been stale for 60 days and will be closed automatically in 7 days. Comment to keep it open.

[pmur]

This is still useful. Ping.

[ryanfoxtyler]

@pmur tests are passing now, though I'm concerned about the maintenance cost of this when we don't have an environment to test on–is that something you're able/willing to help with?

[dmitshur]

In case it's helpful, I'll point out that you can get some signal from compile-only testing via cross-compilation. For example, GOOS=aix GOARCH=ppc64 go test -c -o=/dev/null can be run on any platform you have access to, and at least check for build errors. (The -c flag tells the go command to compile the test binary but do not run it, while the -o flag is used to discard the result, since you only care about the exit code.)

[pmur]

I can provide some help in a limited capacity. Note, I have been using publicly available resources to implement test this (the aix golang CI instance, and the aix gcc compiler farm instance).

I hope @ayappanec might be able to provide more official help. He is part of the IBM team maintaining OSS software on aix.

[ayappanec]

@pmur Thanks for tagging me here.
We are currently in the process of creating new AIX VMs in OSU lab which we give it to various Opensource communities to enable AIX support. I will try to get a VM for this.