This reapplies commit 1911a50fae8a441b445eb835b98950710d28fc88 with a
minor fix in lld/ELF/LTO.cpp which sets Options.BBAddrMap when
`--lto-basic-block-sections=labels` is passed.
This feature is supported via the newer option
`-fbasic-block-address-map`. Using the old option still works by
delegating to the newer option, while a warning is printed to show
deprecation.