Merge from rustc

Author: The Miri Cronjob Bot

src/building/bootstrapping/writing-tools-in-bootstrap.md

@@ -4,7 +4,7 @@ There are three types of tools you can write in bootstrap:
 
 - **`Mode::ToolBootstrap`**
   Use this for tools that don’t need anything from the in-tree compiler and can run with the stage0 `rustc`.
-  The output is placed in the "stage0-bootstrap-tools" directory. This mode is for general-purpose tools built
+  The output is placed in the "bootstrap-tools" directory. This mode is for general-purpose tools built
   entirely with the stage0 compiler, including target libraries and only works for stage 0.
 
 - **`Mode::ToolStd`**

src/tests/ui.md

@@ -113,6 +113,8 @@ Compiletest makes the following replacements on the compiler output:
 - The base directory where the test's output goes is replaced with
   `$TEST_BUILD_DIR`. This only comes up in a few rare circumstances. Example:
   `/path/to/rust/build/x86_64-unknown-linux-gnu/test/ui`
+- The real directory to the standard library source is replaced with `$SRC_DIR_REAL`.
+- The real directory to the compiler source is replaced with `$COMPILER_DIR_REAL`.
 - Tabs are replaced with `\t`.
 - Backslashes (`\`) are converted to forward slashes (`/`) within paths (using a
   heuristic). This helps normalize differences with Windows-style paths.