[coreboot] libpayload: Add -Os to the CFLAGS

[Segher Boessenkool]

> Unfortunately, it exposes a strange issue where strcpy() suddenly goes
> missing - we think that strcpy() is being provided by libgcc, and that
> for some reason, -Os changes the beahavior.

strcpy() isn't part of libgcc.  What happened is that without -Os, the
compiler will inline certain invocations of strcpy() as a builtin.

> +char *strcpy(char *d, const char *s)
> +{
> +	return strncpy(d, s, strlen(s));
> +}

This doesn't put a terminating 0 on the string.


Segher