Fix for configure error in 9.5/9.6 on macOS 11.0 Big Sur

Hello,

Under the next version of macOS (11.0 unreleased beta 3), configuring Postgres 9.5 and 9.6 fails with

> checking test program... ok
> checking whether long int is 64 bits... no
> checking whether long long int is 64 bits... no
> configure: error: Cannot find a working 64-bit integer type.


This has been fixed for Postgres 10 and onwards by the following commit.  It would be nice for this to be back-ported
forpeople building 9.5 or 9.6 on MacOS. 

> commit 1c0cf52b39ca3a9a79661129cff918dc000a55eb
> Author: Peter Eisentraut <peter_e@gmx.net>
> Date:   Tue Aug 30 12:00:00 2016 -0400
>
>     Use return instead of exit() in configure
>
>     Using exit() requires stdlib.h, which is not included.  Use return
>     instead.  Also add return type for main().
>
>     Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
>     Reviewed-by: Thomas Munro <thomas.munro@enterprisedb.com>
>
> diff --git a/config/c-compiler.m4 b/config/c-compiler.m4
> index a7f6773ae1..7d901e1f1a 100644
> --- a/config/c-compiler.m4
> +++ b/config/c-compiler.m4
> @@ -71,8 +71,10 @@ int does_int64_work()
>      return 0;
>    return 1;
>  }
> +
> +int
>  main() {
> -  exit(! does_int64_work());
> +  return (! does_int64_work());
>  }])],
>  [Ac_cachevar=yes],
>  [Ac_cachevar=no],
> diff --git a/config/c-library.m4 b/config/c-library.m4
> index d330b0cf95..0a7452c176 100644
> --- a/config/c-library.m4
> +++ b/config/c-library.m4
> @@ -204,8 +204,10 @@ int does_int64_snprintf_work()
>      return 0;            /* either multiply or snprintf is busted */
>    return 1;
>  }
> +
> +int
>  main() {
> -  exit(! does_int64_snprintf_work());
> +  return (! does_int64_snprintf_work());
>  }]])],
>  [pgac_cv_snprintf_long_long_int_modifier=$pgac_modifier; break],
>  [],
> diff --git a/configure b/configure
> index 55c771a11e..3eb0faf77d 100755
> --- a/configure
> +++ b/configure
> @@ -13594,8 +13594,10 @@ int does_int64_work()
>      return 0;
>    return 1;
>  }
> +
> +int
>  main() {
> -  exit(! does_int64_work());
> +  return (! does_int64_work());
>  }
>  _ACEOF
>  if ac_fn_c_try_run "$LINENO"; then :
> @@ -13676,8 +13678,10 @@ int does_int64_work()
>      return 0;
>    return 1;
>  }
> +
> +int
>  main() {
> -  exit(! does_int64_work());
> +  return (! does_int64_work());
>  }
>  _ACEOF
>  if ac_fn_c_try_run "$LINENO"; then :
> @@ -13770,8 +13774,10 @@ int does_int64_snprintf_work()
>      return 0;            /* either multiply or snprintf is busted */
>    return 1;
>  }
> +
> +int
>  main() {
> -  exit(! does_int64_snprintf_work());
> +  return (! does_int64_snprintf_work());
>  }
>  _ACEOF
>  if ac_fn_c_try_run "$LINENO"; then :

Kindly,
Thomas Gilligan
thomas.gilligan@icloud.com