[Bug bootstrap/92719] MacOS 10.15 Catalina build fails

[iains at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92719

--- Comment #4 from Iain Sandoe <iains at gcc dot gnu.org> ---
(In reply to Nikhil Benesch from comment #3)
> For posterity, I could reproduce this issue even with the suggested
> `./configure` arguments, i.e., excluding the `--enable-multilib` option.

> I worked around the issue by using the ./contrib/download_prerequisites
> script to build in-tree copies of gmp and friends. I suspect there is still
> a bug here, though, when attempting to use the system's libgmp.

There is no "system libgmp" on macOS, perhaps that is the missing piece of the
puzzle?

You have two ways to do this 
(1) build GMP (and friends) and place them somewhere (then use
--with-gmp=/path/to/gmp/prefix).
(2) build GMP (and friends) in-tree (as you have done).

both techniques work for me on catalina (and indeed on every version of OSX I
test on back to 10.4).  They also work on the unreleased macOS11....