Only pass --extern flags for rlibs in target deps directory

[msizanoen1]

It seems like there are proc macros/build scripts using serde: rust-lang/rust#66207 (comment)
This fix the build error by only passing --extern flags for rlibs in target deps directory (if available, otherwise host deps directory).

r? @Manishearth

changelog: none

[Manishearth]

@bors r+

[bors]

📌 Commit dd4e76a has been approved by Manishearth

[bors]

⌛ Testing commit dd4e76a with merge ba280b0...

[Manishearth]

More strongly of the opinion that we should be disabling tests with deps on rustc CI, we CI them locally anyway.

[msizanoen1]

Well, the rustc API interface is incredibly unstable, the API type definition may change and cause compile failure - which should be caught right on rustc CI. However behavior changes in API which causes it not to work as expected would cause the tools test to fail but not caught by rustc CI and test failures for clippy won't be tracked on toolstate.
Behavior API changes probably don't happen often though.

[msizanoen1]

@bors r- dogfood error

error: identical conversion
  --> tests/compile-test.rs:66:25
   |
66 |       let disambiguated = deps
   |  _________________________^
67 | |         .into_iter()
   | |____________________^ help: consider removing `.into_iter()`: `deps`
   |
   = note: `-D clippy::identity-conversion` implied by `-D clippy::all`
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#identity_conversion

[Manishearth]

@bors r-

bors won't listen to you, but if you push to the branch it will autocancel

[msizanoen1]

I thought that authors can unapprove own PR: rust-lang/homu#42

[Manishearth]

Oh, cool, didn't know that. But yeah bors doesn't cancel Travis, it just stops listening to it.

…

On Sat, Nov 9, 2019, 8:31 PM msizanoen1 ***@***.***> wrote: I thought that authors can unapprove own PR: rust-lang/homu#42 <rust-lang/homu#42> — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#4800?email_source=notifications&email_token=AAMK6SCOUHIXSQ2PQT7NVJDQS6FC3A5CNFSM4JLKXVYKYY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEDUVDWQ#issuecomment-552161754>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAMK6SFULSWG7M3HW46Z6ALQS6FC3ANCNFSM4JLKXVYA> .

[msizanoen1]

I am typing this on a mobile device and having a problem with the touch screen, sorry for the spam!

[msizanoen1]

Anyway, I have fixed the dogfood error so this should be ready for review again.

[Manishearth]

@bors r+

[bors]

📌 Commit 805fef0 has been approved by Manishearth

[bors]

⌛ Testing commit 805fef0 with merge 6f9c43d...

[bors]

☀️ Test successful - checks-travis, status-appveyor
Approved by: Manishearth
Pushing 6f9c43d to master...