Properly handle shmget() ENOMEM error conditions on Windows

[cmb69]

We need to properly handle MapViewOfFileEx() failures; otherwise strange error messages might be reported in the following. E.g. bug72858.phpt is likely to fail on 32bit Windows with "Warning: shm_attach(): Failed for key 0x64: File exists".

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Note that this issue also affects older PHP versions, but the chance of MapViewOfFileEx() failing is very small there, because we only tried to map an info segment there, instead of trying to map the whole segment now, due to #8648.

[Lewiscowles1986]

This looks like a really nice fix. Can I ask if there is any desire to get this merged?

Looking into newer PHP build failures on Windows, it does seem that they could be influenced by seemingly small bugs like this fixes.

[krakjoe]

I'm unsure why no CI is running for this ? anyone ?

It looks correct and perfectly reasonable to merge, but I'm reluctant without running tests.

@cmb69 if you're around could you get this to run CI ?

[cmb69]

I have rebased onto current master, and now CI is running. Still not sure whether CI is really helpful here (as far as I know, we have only few tests regarding SHM on Windows). And I can barely remember what this PR is about.