Make sure dd_size is init'd, even when nothing has been read (so it
will be 0). Reported on tech-userlevel by Mouse 20210711T044753+0000

scandir/alphasort take "const struct dirent **" not "const void *" in
modern unix. since we claim to be 'IEEE Std 1003.1-2008', make it so.

PR/45989: Martin Husemann: lint invocation does include -w only on i386

- turn lint -w for all the platforms after fixing the lint warnings.
- add _DIAGASSERTS() for casts that would assign values t

PR/45989: Martin Husemann: lint invocation does include -w only on i386

- turn lint -w for all the platforms after fixing the lint warnings.
- add _DIAGASSERTS() for casts that would assign values to types that
would not fit.
- change types, add casts
- change into ansii prototypes
- turn on _DIAGNOSTIC for libc (during current, to be eliminated for release
builds)

approved by core@

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close on exec fixes:
- open + fcntl -> open O_CLOEXEC
- configuration database file descriptors that can stay open are now opened
fopen(db, "re")

fix rewinddir on nfs. fix PR/42879 (and probably PR/40229.)