Function rustc_codegen_llvm::debuginfo::metadata::use_enum_fallback

pub(in debuginfo::metadata) fn use_enum_fallback(
    cx: &CodegenCx<'_, '_>
) -> bool

DWARF variant support is only available starting in LLVM 8, but on MSVC we have to use the fallback mode, because LLVM doesn't lower variant parts to PDB.