Problem:
`nvim -v` and `:version` prints system vimrc, fallback files, and compilation
info by default, which most people don't care about and just clutters up the
output.
Solution:
Omit extra info unless 'verbose' is set.
Extend the capabilities of is_os to detect more platforms such as
freebsd and openbsd. Also remove `iswin()` helper function as it can be
replaced by `is_os("win")`.
This is essentially a convenience wrapper around the `pending()`
function, similar to `skip_fragile()` but more general-purpose.
Also remove `pending_win32` function as it can be replaced by
`skip(iswin())`.
* Reading from stdin on Windows is fixed in the same way as it was in
#8267.
* The file_read function was returning without filling the
destination buffer when it was called with a non-blocking file
descriptor.
This variant uses `fdopen()` which is not standard, but it fixes problem on my
system. In next commit `scriptin` will use `FileDescriptor*` from os/fileio in
place of `FILE*`.
