selftests/mm: use __auto_type in swap() macro

selftests/mm: use __auto_type in swap() macro

Replace typeof() with __auto_type in the swap() macro in uffd-stress.c.
__auto_type was introduced in GCC 4.9 and reduces the compile time for all
compilers.  No functional changes intended.

Link: https://lkml.kernel.org/r/20250730142301.6754-1-pranav.tyagi03@gmail.com
Signed-off-by: Pranav Tyagi <pranav.tyagi03@gmail.com>
Reviewed-by: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>