kbuild: rust_is_available: check that output looks as expected

The script already checks for `$RUSTC` and `$BINDGEN` existing
and exiting without failure. However, one may still pass an
unexpected binary that does not output what the later parsing
expects. The script still successfully reports a failure as
expected, but the error is confusing. For instance:

    $ RUSTC=true BINDGEN=bindgen CC=clang scripts/rust_is_available.sh
    scripts/rust_is_available.sh: 19: arithmetic expression: expecting primary: "100000 *  + 100 *  + "
    ***
    *** Please see Documentation/rust/quick-start.rst for details
    *** on how to set up the Rust support.
    ***

Thus add an explicit check and a proper message for unexpected
output from the called command.

Similarly, do so for the `libclang` version parsing, too.

Link: https://lore.kernel.org/rust-for-linux/CAK7LNAQYk6s11MASRHW6oxtkqF00EJVqhHOP=5rynWt-QDUsXw@mail.gmail.com/Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Link: https://lore.kernel.org/r/20230616001631.463536-11-ojeda@kernel.orgSigned-off-by: Miguel Ojeda <ojeda@kernel.org>

scripts/rust_is_available.sh

@@ -97,6 +97,15 @@ rust_compiler_version=$( \
 	echo "$rust_compiler_output" \
 		| sed -nE '1s:.*rustc ([0-9]+\.[0-9]+\.[0-9]+).*:\1:p'
 )
+if [ -z "$rust_compiler_version" ]; then
+	echo >&2 "***"
+	echo >&2 "*** Running '$RUSTC' to check the Rust compiler version did not return"
+	echo >&2 "*** an expected output. See output and docs below for details:"
+	echo >&2 "***"
+	echo >&2 "$rust_compiler_output"
+	echo >&2 "***"
+	exit 1
+fi
 rust_compiler_min_version=$($min_tool_version rustc)
 rust_compiler_cversion=$(get_canonical_version $rust_compiler_version)
 rust_compiler_min_cversion=$(get_canonical_version $rust_compiler_min_version)
@@ -136,6 +145,15 @@ rust_bindings_generator_version=$( \
 	echo "$rust_bindings_generator_output" \
 		| sed -nE '1s:.*bindgen ([0-9]+\.[0-9]+\.[0-9]+).*:\1:p'
 )
+if [ -z "$rust_bindings_generator_version" ]; then
+	echo >&2 "***"
+	echo >&2 "*** Running '$BINDGEN' to check the bindings generator version did not return"
+	echo >&2 "*** an expected output. See output and docs below for details:"
+	echo >&2 "***"
+	echo >&2 "$rust_bindings_generator_output"
+	echo >&2 "***"
+	exit 1
+fi
 rust_bindings_generator_min_version=$($min_tool_version bindgen)
 rust_bindings_generator_cversion=$(get_canonical_version $rust_bindings_generator_version)
 rust_bindings_generator_min_cversion=$(get_canonical_version $rust_bindings_generator_min_version)
@@ -184,6 +202,16 @@ bindgen_libclang_version=$( \
 	echo "$bindgen_libclang_output" \
 		| sed -nE 's:.*clang version ([0-9]+\.[0-9]+\.[0-9]+).*:\1:p'
 )
+if [ -z "$bindgen_libclang_version" ]; then
+	echo >&2 "***"
+	echo >&2 "*** Running '$BINDGEN' to check the libclang version (used by the Rust"
+	echo >&2 "*** bindings generator) did not return an expected output. See output"
+	echo >&2 "*** and docs below for details:"
+	echo >&2 "***"
+	echo >&2 "$bindgen_libclang_output"
+	echo >&2 "***"
+	exit 1
+fi
 bindgen_libclang_min_version=$($min_tool_version llvm)
 bindgen_libclang_cversion=$(get_canonical_version $bindgen_libclang_version)
 bindgen_libclang_min_cversion=$(get_canonical_version $bindgen_libclang_min_version)