[MacPorts] #57214: cargo links with libssh2 but does not declare dependency

[MacPorts]

#57214: cargo links with libssh2 but does not declare dependency
------------------------+--------------------
 Reporter:  ryandesign  |      Owner:  (none)
     Type:  defect      |     Status:  new
 Priority:  Normal      |  Milestone:
Component:  ports       |    Version:
 Keywords:              |       Port:  cargo
------------------------+--------------------
 cargo seems to opportunistically link with libssh2 but does not declare a
 dependency on it; this caused l2dy's build of mpv on the Mojave buildbot
 worker to fail at librsvg:

 {{{
 cd ./rust &&                                            \
         PKG_CONFIG_ALLOW_CROSS=1
 \
         PKG_CONFIG='/opt/local/bin/pkg-config'
 \
 CARGO_TARGET_DIR=/opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_graphics_librsvg/librsvg/work/librsvg-2.42.2/rust/target
 \
         cargo build --verbose  --release
 dyld: Library not loaded: /opt/local/lib/libssh2.1.dylib
   Referenced from: /opt/local/bin/cargo
   Reason: image not found
 /bin/sh: line 1: 20881 Abort trap: 6           PKG_CONFIG_ALLOW_CROSS=1
 PKG_CONFIG='/opt/local/bin/pkg-config'
 CARGO_TARGET_DIR=/opt/local/var/macports/build/_opt_bblocal_var_buildworker_ports_build_ports_graphics_librsvg/librsvg/work/librsvg-2.42.2/rust/target
 cargo build --verbose --release
 }}}

 I don't know cargo... should we add the libssh2 dependency, or should we
 make cargo not use libssh2? Whichever we choose, the revision needs to be
 increased.

-- 
Ticket URL: <https://trac.macports.org/ticket/57214>
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