rust: work around bindgen 0.69.0 issue

`bindgen` 0.69.0 contains a bug: `--version` does not work without
providing a header [1]:

    error: the following required arguments were not provided:
      <HEADER>

    Usage: bindgen <FLAGS> <OPTIONS> <HEADER> -- <CLANG_ARGS>...

Thus, in preparation for supporting several `bindgen` versions, work
around the issue by passing a dummy argument.

Include a comment so that we can remove the workaround in the future.

Link: rust-lang/rust-bindgen#2678 [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

scripts/rust_is_available.sh

@@ -121,8 +121,12 @@ fi
 # Check that the Rust bindings generator is suitable.
 #
 # Non-stable and distributions' versions may have a version suffix, e.g. `-dev`.
+#
+# The dummy parameter `workaround-for-0.69.0` is required to support 0.69.0
+# (https://github.com/rust-lang/rust-bindgen/pull/2678). It can be removed when
+# the minimum version is upgraded past that (0.69.1 already fixed the issue).
 rust_bindings_generator_output=$( \
-	LC_ALL=C "$BINDGEN" --version 2>/dev/null
+	LC_ALL=C "$BINDGEN" --version workaround-for-0.69.0 2>/dev/null
 ) || rust_bindings_generator_code=$?
 if [ -n "$rust_bindings_generator_code" ]; then
 	echo >&2 "***"