Add a proc-macro to derive HashStable in librustc dependencies

[cjgillot]

A second proc-macro is added to derive HashStable for crates librustc depends on.
This proc-macro HashStable_Generic (to bikeshed) allows to decouple code and some librustc's boilerplate.

Not everything is migrated, because Span and TokenKind require to be placed inside librustc.
Types using them stay there too.

Split out of #66279
r? @Zoxc

[Zoxc]

@bors r+

[bors]

📌 Commit d4be89b776c930329d6bb5d406df87b6bf1cf537 has been approved by Zoxc

[bors]

☔ The latest upstream changes (presumably #66384) made this pull request unmergeable. Please resolve the merge conflicts.

[rust-highfive]

Your PR failed (pretty log, 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.

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)

[bors]

💔 Test failed - checks-azure

[Centril]

@bors retry spurious network

[bors]

⌛ Testing commit 44a595f with merge 5aef73d5964fcdbf42c79c01ce37fdea07930d0a...

[rust-highfive]

Your PR failed (pretty log, 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.

2019-11-22T00:14:11.3011470Z do so (now or later) by using -b with the checkout command again. Example:
2019-11-22T00:14:11.3012316Z 
2019-11-22T00:14:11.3012460Z   git checkout -b <new-branch-name>
2019-11-22T00:14:11.3012527Z 
2019-11-22T00:14:11.3012635Z HEAD is now at 5aef73d59 Auto merge of #66460 - cjgillot:hashstable_generic, r=Zoxc
2019-11-22T00:14:11.3401254Z ##[section]Starting: Decide whether to run this job
2019-11-22T00:14:11.3517614Z ==============================================================================
2019-11-22T00:14:11.3517732Z Task         : Bash
2019-11-22T00:14:11.3517961Z Description  : Run a Bash script on macOS, Linux, or Windows
---
2019-11-22T00:14:12.6821011Z BUILD_SOURCEBRANCHNAME=auto
2019-11-22T00:14:12.6821104Z BUILD_SOURCESDIRECTORY=D:\a\1\s
2019-11-22T00:14:12.6821191Z BUILD_SOURCEVERSION=5aef73d5964fcdbf42c79c01ce37fdea07930d0a
2019-11-22T00:14:12.6821284Z BUILD_SOURCEVERSIONAUTHOR=bors
2019-11-22T00:14:12.6821380Z BUILD_SOURCEVERSIONMESSAGE=Auto merge of #66460 - cjgillot:hashstable_generic, r=Zoxc
2019-11-22T00:14:12.6821552Z CI_JOB_NAME=dist-x86_64-msvc
2019-11-22T00:14:12.6821791Z COBERTURA_HOME=C:\cobertura-2.1.1
2019-11-22T00:14:12.6821872Z COMMONPROGRAMFILES=C:\Program Files\Common Files
2019-11-22T00:14:12.6821968Z COMMON_TESTRESULTSDIRECTORY=D:\a\1\TestResults
---
2019-11-22T00:14:12.6836743Z TMP=/tmp
2019-11-22T00:14:12.6836821Z TOOLSTATE_ISSUES_API_URL=https://api.github.com/repos/rust-lang/rust/issues
2019-11-22T00:14:12.6836916Z TOOLSTATE_PUBLISH=1
2019-11-22T00:14:12.6836998Z TOOLSTATE_REPO=https://github.com/rust-lang-nursery/rust-toolstate
2019-11-22T00:14:12.6837122Z This proc-macro HashStable_Generic (to bikeshed) allows to decouple code and some librustc's boilerplate.
2019-11-22T00:14:12.6837273Z Types using them stay there too.
2019-11-22T00:14:12.6837459Z USERDOMAIN=fv-az433
2019-11-22T00:14:12.6837527Z USERDOMAIN_ROAMINGPROFILE=fv-az433
2019-11-22T00:14:12.6837609Z USERNAME=VssAdministrator
2019-11-22T00:14:12.6837679Z USERPROFILE=C:\Users\VssAdministrator
---
2019-11-22T00:14:25.5034738Z  35  480M   35  171M    0     0  22.8M      0  0:00:20  0:00:07  0:00:13 24.1M
2019-11-22T00:14:26.8051796Z  40  480M   40  193M    0     0  22.7M      0  0:00:21  0:00:08  0:00:13 23.7M
2019-11-22T00:14:27.1761000Z  44  480M   44  212M    0     0  21.6M      0  0:00:22  0:00:09  0:00:13 21.1M
2019-11-22T00:14:27.1782896Z  46  480M   46  222M    0     0  21.8M      0  0:00:21  0:00:10  0:00:11 21.0M
2019-11-22T00:14:27.1783485Z curl: (56) OpenSSL SSL_read: SSL_ERROR_SYSCALL, errno 10054
2019-11-22T00:14:27.1783761Z 
2019-11-22T00:14:27.1783931Z gzip: stdin: unexpected end of file
2019-11-22T00:14:27.1792289Z tar: Unexpected EOF in archive
2019-11-22T00:14:27.1792406Z tar: Unexpected EOF in archive
2019-11-22T00:14:27.1792499Z tar: Error is not recoverable: exiting now
2019-11-22T00:14:27.1879030Z 
2019-11-22T00:14:27.1961616Z ##[error]Bash exited with code '2'.
2019-11-22T00:14:27.2229443Z ##[section]Starting: Checkout
2019-11-22T00:14:27.2410055Z ==============================================================================
2019-11-22T00:14:27.2410175Z Task         : Get sources
2019-11-22T00:14:27.2410261Z Description  : Get sources from a repository. Supports Git, TfsVC, and SVN repositories.

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)

[bors]

💔 Test failed - checks-azure

[Zoxc]

@bors retry

[bors]

⌛ Testing commit 44a595f with merge 083b5a0...

[bors]

☀️ Test successful - checks-azure
Approved by: Zoxc
Pushing 083b5a0 to master...