Rollup merge of rust-lang#41639 - ishitatsuyuki:unify-tools, r=alexcrichton

Unify tools building

Close rust-lang#41601

Time saving for up to 10 minutes. Cargo is now only compiled once.

Downsides:

- Out of tree Cargo.lock maintenance
- Cargo.toml `[replace]` version maintenance

Author: Mark-Simulacrum

.gitmodules

@@ -23,7 +23,7 @@
 	url = https://github.com/rust-lang-nursery/nomicon.git
 [submodule "src/tools/cargo"]
 	path = src/tools/cargo
-	url = https://github.com/rust-lang/cargo
+	url = https://github.com/rust-lang/cargo.git
 [submodule "reference"]
 	path = src/doc/reference
 	url = https://github.com/rust-lang-nursery/reference.git
@@ -32,4 +32,4 @@
 	url = https://github.com/rust-lang/book.git
 [submodule "src/tools/rls"]
 	path = src/tools/rls
-	url = https://github.com/rust-lang-nursery/rls
+	url = https://github.com/rust-lang-nursery/rls.git