[Bug bootstrap/65150] [5 Regression] r220875 causes bootstrap failure on x86_64 darwin

[howarth at bromo dot med.uc.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65150

--- Comment #15 from howarth at bromo dot med.uc.edu ---
(In reply to Iain Sandoe from comment #14)

> FWIW, LGTM (with suitable guards added to the tests for the target alias
> support).
> (I cannot officially approve of course ;) )
>  ... if we find other regressions a new PR can be opened.

Does this even need approval from a Darwin maintainer (as it doesn't seem to
touch darwin-specific files at all)?