selftests/mm: kvm, mdwe fixes to avoid requiring "make headers"

On Ubuntu 23.04, the kvm and mdwe selftests/mm build fails due to
missing a few items that are found in prctl.h. Here is an excerpt of the
build failures:

ksm_tests.c:252:13: error: use of undeclared identifier 'PR_SET_MEMORY_MERGE'
...
mdwe_test.c:26:18: error: use of undeclared identifier 'PR_SET_MDWE'
mdwe_test.c:38:18: error: use of undeclared identifier 'PR_GET_MDWE'

Fix these errors by adding a new tools/include/uapi/linux/prctl.h . This
file was created by running "make headers", and then copying a snapshot
over from ./usr/include/linux/prctl.h, as per the approach we settled on
in [1].

[1] commit e076eaca ("selftests: break the dependency upon local
header files")

Link: https://lkml.kernel.org/r/20240618022422.804305-6-jhubbard@nvidia.comSigned-off-by: John Hubbard <jhubbard@nvidia.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Andrei Vagin <avagin@google.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jeff Xu <jeffxu@chromium.org>
Cc: Kees Cook <kees@kernel.org>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Rich Felker <dalias@libc.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>