bug#47951: 28.0.50; Recent seccomp changes break compilation in Docker

[Philipp Stephani <p.stephani2@gmail.com>]

Am Do., 22. Apr. 2021 um 15:44 Uhr schrieb <me@mpsq.org>:
>
>
> Hi,
>
> Since the recent changes introduced by Philipp Stephani on seccomp (around
> commit be8328acf9aa464f848e682e63e417a18529af9e), compiling Emacs from within a
> Docker container fails.
>
> The reported error is:
>
> seccomp-filter.c:168:11: error: static_assert expression is not an integral constant expression
>   verify ((uintptr_t) NULL == 0);
>   ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
> ../lib/verify.h:273:32: note: expanded from macro 'verify'
> # define verify(R) _GL_VERIFY (R, "verify (" #R ")", -)
>                    ~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
> ../lib/verify.h:213:57: note: expanded from macro '_GL_VERIFY'
> # define _GL_VERIFY(R, DIAGNOSTIC, ...) _Static_assert (R, DIAGNOSTIC)
>                                                         ^
> seccomp-filter.c:168:11: note: cast that performs the conversions of a reinterpret_cast is not allowed in a constant expression

Looks like the compiler is right, and mine is a bit too lenient. I've
hopefully fixed this with commit
aaf6b6bf80805d18180e1c16350e9473716f5915.