bsd-user: Add syscall header generator for FreeBSD

Generate the syscall numbers from the installed header that has them.
Ideally, we'd use FreeBSD's lua infra for this, but that requires that
we have those files installed, and they aren't quite the same across
supported versions yet, so use this simple, but effective hack. Add to
meson build, but unused.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>
Signed-off-by: Warner Losh <imp@bsdimp.com>

bsd-user/freebsd/meson.build

@@ -1,6 +1,12 @@
+bsd_syscall_nr = custom_target('bsd-syscall-h',
+    output: '@BASENAME@_nr.h',
+    input: ['/usr/include/sys/syscall.h'],
+    command: [sh, meson.current_source_dir() / 'scripts/syscallhdr.sh', '@INPUT@', '@OUTPUT@', 'FREEBSD'])
+
 bsd_user_ss.add(files(
   'os-stat.c',
   'os-proc.c',
   'os-sys.c',
-  'os-syscall.c',
-))
+  'os-syscall.c'),
+  bsd_syscall_nr
+)

bsd-user/freebsd/scripts/syscallhdr.sh

@@ -0,0 +1,9 @@
+#!/bin/sh
+# Copyright (c) 2026 Warner Losh <imp@bsdimp.com>
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+in="$1"
+out="$2"
+bsd="$3"
+
+awk -v bsd="$3" '{sub("SYS_", "TARGET_" bsd "_NR_", $0); print;}' < $in > $out