Rollup merge of #88951 - ehuss:update-books, r=ehuss

Update books

## rust-by-example

1 commits in 04f489c889235fe3b6dfe678ae5410d07deda958..9d4132b56c4999cd3ce1aeca5f1b2f2cb0d11c24
2021-08-17 08:01:20 -0300 to 2021-09-14 06:56:00 -0300
- Fix link to "integration testing" page (rust-lang/rust-by-example#1458)

## rustc-dev-guide

17 commits in 95f1acf9a39d6f402f654e917e2c1dfdb779c5fc..9198465b6ca8bed669df0cbb67c0e6d0b140803c
2021-08-31 12:38:30 -0500 to 2021-09-12 11:50:44 -0500
- Clarify difference of a help vs note diagnostic.
- remove ctag section
- Update suggested.md
- Update SUMMARY.md
- Move ctag section to "Suggested Workflow"
- Delete ctags.md
- Clarify paragraph in "Keeping things up to date"
- Docs: added section on rustdoc
- Docs: made suggested fix
- Docs: deleted copy
- Docs: added section discussing core ideas
- Docs: delete redundant use of correctness
- Docs: consolidated parallelism information
- Add links to overview.md (rust-lang/rustc-dev-guide#1202)
- Spelling change intermidiate to intermediate
- Fix a typo (rust-lang/rustc-dev-guide#1200)
- Documenting diagnostic items with their usage and naming conventions (rust-lang/rustc-dev-guide#1192)

## embedded-book

1 commits in c3a51e23859554369e6bbb5128dcef0e4f159fb5..4c76da9ddb4650203c129fceffdea95a3466c205
2021-08-26 07:04:58 +0000 to 2021-09-12 12:43:03 +0000
- 2.1(QEMU): update app name for git project init  (rust-embedded/book#301)

src/doc/embedded-book

@@ -1 +1 @@
-Subproject commit c3a51e23859554369e6bbb5128dcef0e4f159fb5
+Subproject commit 4c76da9ddb4650203c129fceffdea95a3466c205

src/doc/rust-by-example

@@ -1 +1 @@
-Subproject commit 04f489c889235fe3b6dfe678ae5410d07deda958
+Subproject commit 9d4132b56c4999cd3ce1aeca5f1b2f2cb0d11c24

src/doc/rustc-dev-guide

@@ -1 +1 @@
-Subproject commit 95f1acf9a39d6f402f654e917e2c1dfdb779c5fc
+Subproject commit 9198465b6ca8bed669df0cbb67c0e6d0b140803c