Encode TraitAlias as if they were Trait

[estebank]

Fix #56539.

[rust-highfive]

r? @davidtwco

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[davidtwco]

@bors r+

[bors]

📌 Commit 14cca29 has been approved by davidtwco

[bors]

⌛ Testing commit 14cca29 with merge bc9698c...

[bors]

💔 Test failed - status-travis

[rust-highfive]

The job dist-i686-apple of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:02:27]       Memory: 8 GB
[00:02:27]       Boot ROM Version: VMW71.00V.0.B64.1704110547
[00:02:27]       Apple ROM Info: [MS_VM_CERT/SHA1/27d66596a61c48dd3dc7216fd715126e33f59ae7]Welcome to the Virtual Machine
[00:02:27]       SMC Version (system): 2.8f0
[00:02:27]       Serial Number (system): VMexDW2+RkZr
[00:02:27] 
[00:02:27] hw.ncpu: 4
[00:02:27] hw.byteorder: 1234
[00:02:27] hw.memsize: 8589934592
---
[00:07:47] [RUSTC-TIMING] rustc_errors test:false 40.376
[00:09:33] [RUSTC-TIMING] syntax test:false 105.521
[00:09:33]    Compiling syntax_ext v0.0.0 (/Users/travis/build/rust-lang/rust/src/libsyntax_ext)
[00:10:17] [RUSTC-TIMING] syntax_ext test:false 44.638
No output has been received in the last 30m0s, this potentially indicates a stalled build or something wrong with the build itself.
Check the details on how to adjust your build configuration on: https://docs.travis-ci.com/user/common-build-problems/#Build-times-out-because-no-output-was-received
The build has been terminated

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[davidtwco]

@bors retry

[bors]

⌛ Testing commit 14cca29 with merge 8db2342...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: davidtwco
Pushing 8db2342 to master...