Functions marked with #[no_mangle] are not GC-ed on powerpc

Newly introduced test by this commit fails for powerpc target.
The code used from this issue report also fails to link on powerpc target, due to unresolved symbols.

I tried this code:

// src/main.rs

unsafe extern "C" {
    unsafe static UNDEFINED: usize;
}

#[unsafe(no_mangle)]
pub fn used() {
    println!("UNDEFINED = {}", unsafe { UNDEFINED });
}

pub fn marker() -> usize {
    0
}

fn main() {
    assert_eq!(marker(), 0_usize);
}
cargo build --target powerpc-unknown-linux-gnu

I expected to see this happen: it builds

Instead, this happened: it emits linker errors

error: linking with `powerpc-linux-gnu-gcc` failed: exit status: 1
  |
  = note:  "powerpc-linux-gnu-gcc" "-m32" "/tmp/rustcgCiFys/symbols.o" "<8 object files omitted>" "-Wl,--as-needed" "-Wl,-Bstatic" "<sysroot>/lib/rustlib/powerpc-unknown-linux-gnu/lib/{libstd-*,libpanic_unwind-*,libobject-*,libmemchr-*,libaddr2line-*,libgimli-*,librustc_demangle-*,libstd_detect-*,libhashbrown-*,librustc_std_workspace_alloc-*,libminiz_oxide-*,libadler2-*,libunwind-*,libcfg_if-*,liblibc-*,librustc_std_workspace_core-*,liballoc-*,libcore-*,libcompiler_builtins-*}.rlib" "-Wl,-Bdynamic" "-lgcc_s" "-lutil" "-lrt" "-lpthread" "-lm" "-ldl" "-lc" "-L" "/tmp/rustcgCiFys/raw-dylibs" "-Wl,--eh-frame-hdr" "-Wl,-z,noexecstack" "-L" "<sysroot>/lib/rustlib/powerpc-unknown-linux-gnu/lib" "-o" "/home/projects/rust-test/target/powerpc-unknown-linux-gnu/debug/deps/test_rust-3c4b8a270f49f452" "-Wl,--gc-sections" "-pie" "-Wl,-z,relro,-z,now" "-nodefaultlibs"
  = note: some arguments are omitted. use `--verbose` to show all linker arguments
  = note: /usr/lib/gcc-cross/powerpc-linux-gnu/12/../../../../powerpc-linux-gnu/bin/ld: /home/projects/rust-test/target/powerpc-unknown-linux-gnu/debug/deps/test_rust-3c4b8a270f49f452.42850mbhj0t4hj3povrah4dmz.1ofm0p2.rcgu.o:(.got2+0x0): undefined reference to `UNDEFINED'
          collect2: error: ld returned 1 exit status

  = note: some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
  = note: use the `-l` flag to specify native libraries to link
  = note: use the `cargo:rustc-link-lib` directive to specify the native libraries to link with Cargo (see https://doc.rust-lang.org/cargo/reference/build-scripts.html#rustc-link-lib)

error: could not compile `test-rust` (bin "test-rust") due to 1 previous error

Meta

rustc --version --verbose:

rustc 1.88.0 (6b00bc388 2025-06-23)

Start with the reproduction in src/main.rs and run cargo build --target powerpc-unknown-linux-gnu to confirm the unresolved UNDEFINED symbol. Compare the newly introduced test in the linked commit with the powerpc failure and trace the no_mangle and linker garbage-collection behavior. Done means the test and example link successfully for the powerpc target.