[PATCH] Fix compile error in configure script

[Edgar Bonet]

Hello!

Sergey Kandaurov wrote:
> > objs/autotest.c:9:48: error: passing argument 1
> > of 'AO_compare_and_swap' from incompatible pointer type
> > [-Wincompatible-pointer-types]
> 
> Where did you try to build?

I experienced this when building for arm and i686, both cross-compiled
from x86_64. Building for x86_64 works fine.

> Usually, long and size_t (a "common default" for AO_t) have the same
> underlying type, unless you build with something like MSVC.

AO_t is a 'volatile size_t'. The volatile qualifier may not matter
though. The error message about incompatible types was followed by
this note:

    expected 'volatile size_t *' {aka 'volatile unsigned int *'}
    but argument is of type 'long int *'

My understanding is that the compiler considers 'int' and 'long' to be
incompatible types, even though they have the same underlying
representation on ILP32 environments. I'm not a language lawyer, so I
cannot tell _why_ they are considered incompatible. But then, 'size_t'
being an 'unsigned int', it is incompatible with 'long'.

On LP64 (your typical 64-bit Linux/Mac), 'size_t' is a 'unsigned long',
which is compatible with 'long' but for the signedness warning.

Regards,

Edgar.