Fixes 2 failing tests in startup_spec.lua.
The Windows-only `--literal` option complicates support of "stdin-as-text
+ file-args" (#7679). Could work around it, but it's not worth
the trouble:
- users have a reasonable (and englightening) alternative: nvim +"n *"
- "always literal" is more consistent/predictable
- avoids platform-specific special-case
Unrelated changes:
- Replace fileno(stdxx) with STDXX_FILENO for consistency (not motivated
by any observed technical reason).