Fallback on unix filesystem's remove_dir_impl for target vxworks

[biabbas]

Hi all,
I'm skipping the unix filesystem remove_dir_impl for target vxworks. As seen in the error #127084, remove_dir_impl need libc imports fdopendir, openat, unlinkat. These need to be introduced in libc and tested for vxworks. Thus we are temporarily falling back on remove_dir_impl as our priority is to get a successful build on vxworks.

Thank you.

[rustbot]

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[biabbas]

This pr was merged into PR #127195