pkg/54250: "rust" package fails to build under macOS Mojave

[tron%zhadum.org.uk@localhost]

>Number:         54250
>Category:       pkg
>Synopsis:       "rust" package fails to build under macOS Mojave
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    pkg-manager
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu May 30 10:15:00 +0000 2019
>Originator:     tron%zhadum.org.uk@localhost
>Release:        Darwin 17.7.0 pkgsrc HEAD from 2019-05-29
>Organization:
>Environment:
System: Darwin excalibur.zhadum.org.uk 17.7.0 Darwin Kernel Version 17.7.0: Wed Apr 24 21:17:24 PDT 2019; root:xnu-4570.71.45~1/RELEASE_X86_64 x86_64

macOS Mojave 10.14.5

>Description:
Building the "lang/rust" package fails under macOS Mojave for me:

y file for linking.
          Undefined symbols for architecture x86_64:
            "___isOSVersionAtLeast", referenced from:
                _darwinssl_connect_common in libcurl_sys-b65ef28c9739dfd0.rlib(darwinssl.o)
                _darwinssl_connect_step2 in libcurl_sys-b65ef28c9739dfd0.rlib(darwinssl.o)
          ld: symbol(s) not found for architecture x86_64
          clang: error: linker command failed with exit code 1 (use -v to see invocation)


error: aborting due to previous error

error: Could not compile `cargo`.

This seems to be related:
https://github.com/sfackler/cargo-tree/issues/58

>How-To-Repeat:
cd pkgsrc/lang/rust
bmake

>Fix:
Not known