windows: in mkwinsyscall, add an option to specify a custom dll extension

[ranganath42]

windows: in mkwinsyscall, add an option to specify a custom dll extension

The current implementation uses a hardcoded '.dll' extension, but some
Windows dll files have different extensions (such as .ocx, .drv).

Fixes #58337

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Message from Alex Brainman:

Patch Set 1: Run-TryBot+1

(7 comments)

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Patch Set 1:

(1 comment)

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Patch Set 1: TryBot-Result+1

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