meson: drop arch filtering in syscall list

I added the filtering in 752fedb as a way
to reduce the number of items in the tables. I thought it's "obvious", but
it might not be so.

One immediate problem is that the filter is broken, because on arm64,
os.uname().machine returns "aarch64", so we incorrectly filter out the arm
syscalls (there is just one: arm_fadvise64_64). Of course we could fix the
filter, but I think it's better to nuke it altogether. The filter on applies to
1 arm syscall and 5 s390 syscalls, and we have 500+ other syscalls, so this
"optimization" doesn't really matter. OTOH, if we get the filter wrong,
the result is bad. And also, the existence of the filter at all creates
problems for cross-builds.

I wanted to get rid of 'generate-syscall-list.py', but we need to generate a
backslash in the output. mesonbuild/meson#1564 makes
this very very hard, since any attempt to put a backslash an inline argument
results in the backslash being replaces by a forward slash, which doesn't quite
have the same meaning. So let's use a standalone script until
mesonbuild/meson#1564 is resolved.

(cherry picked from commit 58fcc6b)

src/shared/generate-syscall-list.py

@@ -2,15 +2,6 @@
 # SPDX-License-Identifier: LGPL-2.1-or-later
 
 import sys
-import os
-
-s390 = 's390' in os.uname().machine
-arm = 'arm' in os.uname().machine
 
 for line in open(sys.argv[1]):
-    if line.startswith('s390_') and not s390:
-        continue
-    if line.startswith('arm_') and not arm:
-        continue
-
     print('"{}\\0"'.format(line.strip()))