bug#50666: 28.0.50; Fix native compilation on Cygwin

[ASSI]

Eli Zaretskii writes:
> This means that the following situation will predictably fail:
>
>   . Emacs session A (or just some shell command) rebases a .eln file
>   . Emacs session B decides it needs to load that .eln
>
> What kind of failure will session B see in this case?  Is it possible
> to figure out somehow that this is the reason, so that we could
> instead try loading the .elc or .el?

Something like EPERM I'd think, and only very briefly (i.e. if you tretry
the exact same call it will usually succeed).  We could rename the file
while operating on it, but that just moves the point of where the file
system race is happening and makes the window a tiny bit smaller.

What do you do on Linux in the case that two processes try to generate
the same .eln?


Regards,
Achim.
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