Rust 1.44.0.0 won't compile on macOS Sierra 10.12.6 and Trac ticket # 56351

[Greg Earle]

I did a "port upgrade outdated" and it looks like "librsvg" has a 
dependency on Cairo which in turn pulls in Rust.  (I didn't have Rust 
installed previously.)

There don't seem to be any pre-made Rust binary bundles for Sierra, so 
it tries to build it from src and fails:

--
sudo port install rust
[...]
--->  Building rust
Error: Failed to build rust: command execution failed
Error: See 
/opt/local/var/macports/logs/_private_opt_local_var_macports_sources_rsync.macports.org_release_tarballs_ports_lang_rust/rust/main.log 
for details.
Error: Follow https://guide.macports.org/#project.tickets to report a 
bug.
Error: Processing of port rust failed
--

I seem to be hitting the same issue as described by Marcus Calhoun-Lopez 
back in 2018:

https://trac.macports.org/ticket/56351

https://github.com/rust-lang/rust/issues/50220

but that bug report was for High Sierra 10.13.4.

Most of the additions from his workaround in commit

https://github.com/macports/macports-ports/commit/e429b4d8a8b2667f23110596fbe7ebee9f28d72e

don't seem to be in the present rust/Portfile, which seems to have 
varied enough from the one he based his commit on that I'm not 
comfortable changing anything.

Is the only (other) workaround to de-activate llvm-9.0 +universal?

--
# port installed | grep llvm-
   llvm-3.3 @3.3_10 (active)
   llvm-6.0 @6.0.1_1 (active)
   llvm-7.0 @7.1.0_0 (active)
   llvm-8.0 @8.0.1_0 (active)
   llvm-9.0 @9.0.1_0+universal (active)
--

Thanks,

		- Greg