Building bgrep in release mode fails with linker errors

[bjorn3]

https://github.com/gahag/bgrep

Reported by @jyn514 in https://github.com/bjorn3/rustc_codegen_cranelift/issues/247#issuecomment-540092766

[bjorn3]

Full log at https://gist.github.com/bjorn3/d76a88ce2ea1a6d54e278c59853056d5

[bjorn3]

The relevant rlibs seem to export at least several of the symbols which the linker thinks are undefined.

[bjorn3]

I diffed the linker invocation and the only diff is that cg_clif codegens the allocator shim, while cg_llvm doesn't. This can't be the source of this problem though.

[bjorn3]

bgrep uses LTO in release mode. This doesn't work with cg_clif. See https://github.com/bjorn3/rustc_codegen_cranelift/issues/779#issuecomment-575661625 for more info.