[MacPorts] #63333: cargo @0.54.0_1 fails to build some crates on 10.9

[MacPorts]

#63333: cargo @0.54.0_1 fails to build some crates on 10.9
-----------------------+---------------------------------------
 Reporter:  fhgwright  |      Owner:  herbygillot
     Type:  defect     |     Status:  assigned
 Priority:  Normal     |  Milestone:
Component:  ports      |    Version:  2.7.1
 Keywords:             |       Port:  cargo, rust-compiler-wrap
-----------------------+---------------------------------------
 This bug is probably actually in `rust-compiler-wrap @1.54.0`, though it's
 observed with the `cargo` command.

 When attempting to build `library-loader-cli` in accordance with the
 instructions at https://github.com/olback/library-loader, three crates
 fail to build: `bzip2-sys`, `serde_derive`, and `failure_derive`.  The
 failures are all link failures attempting to reference `_linkat`, which is
 a call that the OS doesn't support until 10.10.

 The port attempts to use `legacy-support` to handle such cases, and the
 fact that the failure occurs at link time rather than compile time
 indicates that the headers are wrapped properly, but that the proper
 library specification doesn't happen.

-- 
Ticket URL: <https://trac.macports.org/ticket/63333>
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