rust: Simple main wrapper

Until further variants are needed, this provides a `main()` function
that simply calls into the `rust_main()` function.  This is adequate for
applications where main can be directly written in Rust.

The reason that this is written here, rather than just writing `main`
directly in Rust is that `kernel/main_weak.c` provides a weak default
implementation that will be brought in before the Rust application's
`main` is linked in.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

lib/rust/main.c

@@ -0,0 +1,18 @@
+/*
+ * Copyright (c) 2024 Linaro LTD
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+/* This main is brought into the Rust application. */
+
+#ifdef CONFIG_RUST
+
+extern void rust_main(void);
+
+int main(void)
+{
+	rust_main();
+	return 0;
+}
+
+#endif