-Clinker-plugin-lto breaks with -Copt-level=s/z

[jonas-schievink]

$ cat main.rs
fn main() {
    println!("Hello World!");
}

Using the instructions at https://doc.rust-lang.org/stable/rustc/linker-plugin-lto.html#cc-code-as-a-dependency-in-rust.

Works fine with numerical opt-levels:

$ rustc main.rs -Clinker-plugin-lto -Clinker=clang -Clink-arg=-fuse-ld=lld -Copt-level=3

Breaks with -Copt-level=s/z:

$ rustc main.rs -Clinker-plugin-lto -Clinker=clang -Clink-arg=-fuse-ld=lld -Copt-level=s
error: linking with `clang` failed: exit code: 1
  |
  = note: "clang" "-Wl,--as-needed" "-Wl,-z,noexecstack" "-m64" "-Wl,-plugin-opt=Oz" "-Wl,-plugin-opt=mcpu=x86-64" "-L" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "main.main.7rcbfp3g-cgu.0.rcgu.o" "main.main.7rcbfp3g-cgu.1.rcgu.o" "-o" "main" "main.4s37gsrti678ik8u.rcgu.o" "-Wl,--gc-sections" "-pie" "-Wl,-zrelro" "-Wl,-znow" "-nodefaultlibs" "-L" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib" "-Wl,--start-group" "-Wl,-Bstatic" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libstd-c147cd9c030850ef.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libpanic_unwind-7e62a3a07bb85bc1.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libhashbrown-000f77165d4d2d36.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_alloc-7dc0cb59ed386ac6.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libbacktrace-9248bfbd7273ac3d.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libbacktrace_sys-b75363fb938de39d.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_demangle-7bbe96f555da4ad6.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libunwind-a145493c64eeb044.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcfg_if-9577436fc6fce6bc.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liblibc-b3376c0a2b35415c.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/liballoc-5708f6b2b59b6e0f.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/librustc_std_workspace_core-e9fd09201d99d6f4.rlib" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcore-914c6ef6f5cf354a.rlib" "-Wl,--end-group" "/home/jonas/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/lib/libcompiler_builtins-1445b6c7903692a2.rlib" "-Wl,-Bdynamic" "-ldl" "-lrt" "-lpthread" "-lgcc_s" "-lc" "-lm" "-lrt" "-lpthread" "-lutil" "-ldl" "-lutil" "-fuse-ld=lld"
  = note: ld.lld: error: -plugin-opt=Oz: number expected, but got 'z'
          clang-10: error: linker command failed with exit code 1 (use -v to see invocation)