Patch to enable -Werror [take 2]

[Rainer Orth]

Zack Weinberg writes:

> I see that I suggested an autoconf test for the typedef at the time.
> What is the underlying definition of uchar on AIX and Tru64 Unix?  I
> am hesitant to use it in case it turns out not to be unsigned char
> reliably.

On both Tru64 UNIX V4.0F and V5.1, <sys/types.h> has

typedef unsigned char   uchar_t;
typedef uchar_t         uchar;

	Rainer