OK, the magic you need to use .gnu.sgstubs on LLD with our linker script is:

```rust
    println!("cargo:rustc-link-arg=--cmse-implib");
    println!("cargo:rustc-link-arg=--section-start=.gnu.sgstubs=0x0C1F0000");
    println!("cargo:rustc-link-arg=--out-implib=target/libsec_bootloader_stubs.o");
```