kbuild: avoid scripts/kallsyms parsing /dev/null

On macOS, as reported by Daniel Gomez, getline() sets ENOTTY to errno
if it is requested to read from /dev/null.

If this is worth fixing, I would rather pass an empty file to
scripts/kallsyms instead of adding the ugly #ifdef __APPLE__.

Fixes: c442db3 ("kbuild: remove PROVIDE() for kallsyms symbols")
Reported-by: Daniel Gomez <da.gomez@samsung.com>
Closes: https://lore.kernel.org/all/20240807-macos-build-support-v1-12-4cd1ded85694@samsung.com/
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
Reviewed-by: Daniel Gomez <da.gomez@samsung.com>

scripts/link-vmlinux.sh

@@ -219,7 +219,8 @@ kallsymso=
 strip_debug=
 
 if is_enabled CONFIG_KALLSYMS; then
-	kallsyms /dev/null .tmp_vmlinux0.kallsyms
+	truncate -s0 .tmp_vmlinux.kallsyms0.syms
+	kallsyms .tmp_vmlinux.kallsyms0.syms .tmp_vmlinux0.kallsyms
 fi
 
 if is_enabled CONFIG_KALLSYMS || is_enabled CONFIG_DEBUG_INFO_BTF; then