[Toybox] Issues - deprecated bzero and xread

[Rob Landley]

> Hi I get warnings / errors with non glibc libcs, specifically with
> musl libc in main.c:84, lib/args.c:160, lib.c:94 and toys/toysh.c:294
> all due to use of bzero.

Which is 4 bytes smaller than memset(x, 0, len) on 32 bit platforms (and
8 on 64 bit platforms) due to needing one less argument.  memset with
zero is the common case.

I can wrap it myself in libbb and stick glue in lib/portability.h to
figure out when to need to do it.  But basically, deprecating it was
stupid, and if they take it out of libc I'll put it back in lib/lib.c.

> Also xread in lib.* should be ssize_t?

Yeah, that's a bug.  It needs a local signed variable.

As for the arguments: it can't read a negative amount, and doesn't ever
return a negative value, so the non-signed size_t is fine.  (It's
intentional, note that readall() and writeall() return ssize_t.)

But since _read_ has different semantics than xread(), we need a
differnet variable for its return value.  Good catch, thanks.

In theory main() should be setting up the SA_RESTART stuff described in
sigaction so we're not constantly checking for EAGAIN.  In practice
that's a todo item...

Rob

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