aio: Combine io_uring memory mappings, if supported

By default io_uring creates a shared memory mapping for each io_uring
instance, leading to a large number of memory mappings. Unfortunately a large
number of memory mappings slows things down, backend exit is particularly
affected.  To address that, newer kernels (6.5) support using user-provided
memory for the memory. By putting the relevant memory into shared memory we
don't need any additional mappings.

On a system with a new enough kernel and liburing, there is no discernible
overhead when doing a pgbench -S -C anymore.

Reported-by: MARK CALLAGHAN <mdcallag@gmail.com>
Reviewed-by: "Burd, Greg" <greg@burd.me>
Reviewed-by: Jim Nasby <jnasby@upgrade.com>
Discussion: https://postgr.es/m/CAFbpF8OA44_UG+RYJcWH9WjF7E3GA6gka3gvH6nsrSnEe9H0NA@mail.gmail.com
Backpatch-through: 18

configure

@@ -13309,6 +13309,23 @@ fi
 
 fi
 
+if test "$with_liburing" = yes; then
+  _LIBS="$LIBS"
+  LIBS="$LIBURING_LIBS $LIBS"
+  for ac_func in io_uring_queue_init_mem
+do :
+  ac_fn_c_check_func "$LINENO" "io_uring_queue_init_mem" "ac_cv_func_io_uring_queue_init_mem"
+if test "x$ac_cv_func_io_uring_queue_init_mem" = xyes; then :
+  cat >>confdefs.h <<_ACEOF
+#define HAVE_IO_URING_QUEUE_INIT_MEM 1
+_ACEOF
+
+fi
+done
+
+  LIBS="$_LIBS"
+fi
+
 if test "$with_lz4" = yes ; then
   { $as_echo "$as_me:${as_lineno-$LINENO}: checking for LZ4_compress_default in -llz4" >&5
 $as_echo_n "checking for LZ4_compress_default in -llz4... " >&6; }