Minor updates to stage docs. (#781)

Author: ehuss

src/building/bootstrapping.md

@@ -128,7 +128,7 @@ The following tables indicate the outputs of various stage actions:
 |-----------------------------------------------------------|----------------------------------------------|
 | `beta` extracted                                          | `build/HOST/stage0`                          |
 | `stage0` builds `bootstrap`                               | `build/bootstrap`                            |
-| `stage0` builds `libstd`                                  | `build/HOST/stage0-std/TARGET`               |
+| `stage0` builds `libtest`/`libstd`                        | `build/HOST/stage0-std/TARGET`               |
 | copy `stage0-std` (HOST only)                             | `build/HOST/stage0-sysroot/lib/rustlib/HOST` |
 | `stage0` builds `rustc` with `stage0-sysroot`             | `build/HOST/stage0-rustc/HOST`               |
 | copy `stage0-rustc (except executable)`                   | `build/HOST/stage0-sysroot/lib/rustlib/HOST` |
@@ -143,22 +143,22 @@ The following tables indicate the outputs of various stage actions:
 | copy (uplift) `stage0-rustc` executable to `stage1` | `build/HOST/stage1/bin`               |
 | copy (uplift) `stage0-codegen` to `stage1`          | `build/HOST/stage1/lib`               |
 | copy (uplift) `stage0-sysroot` to `stage1`          | `build/HOST/stage1/lib`               |
-| `stage1` builds `libstd`                            | `build/HOST/stage1-std/TARGET`        |
+| `stage1` builds `libtest`/`libstd`                  | `build/HOST/stage1-std/TARGET`        |
 | copy `stage1-std` (HOST only)                       | `build/HOST/stage1/lib/rustlib/HOST`  |
 | `stage1` builds `rustc`                             | `build/HOST/stage1-rustc/HOST`        |
 | copy `stage1-rustc` (except executable)             | `build/HOST/stage1/lib/rustlib/HOST`  |
 | `stage1` builds `codegen`                           | `build/HOST/stage1-codegen/HOST`      |
 
 `--stage=1` stops here.
 
-| Stage 2 Action                            | Output                                                          |
-|-------------------------------------------|-----------------------------------------------------------------|
-| copy (uplift) `stage1-rustc` executable   | `build/HOST/stage2/bin`                                         |
-| copy (uplift) `stage1-sysroot`            | `build/HOST/stage2/lib and build/HOST/stage2/lib/rustlib/HOST`  |
-| `stage2` builds `libstd` (except HOST?)   | `build/HOST/stage2-std/TARGET`                                  |
-| copy `stage2-std` (not HOST targets)      | `build/HOST/stage2/lib/rustlib/TARGET`                          |
-| `stage2` builds `rustdoc`                 | `build/HOST/stage2-tools/HOST`                                  |
-| copy `rustdoc`                            | `build/HOST/stage2/bin`                                         |
+| Stage 2 Action                                         | Output                                                          |
+|--------------------------------------------------------|-----------------------------------------------------------------|
+| copy (uplift) `stage1-rustc` executable                | `build/HOST/stage2/bin`                                         |
+| copy (uplift) `stage1-sysroot`                         | `build/HOST/stage2/lib and build/HOST/stage2/lib/rustlib/HOST`  |
+| `stage2` builds `libtest`/`libstd` (not HOST targets)  | `build/HOST/stage2-std/TARGET`                                  |
+| copy `stage2-std` (not HOST targets)                   | `build/HOST/stage2/lib/rustlib/TARGET`                          |
+| `stage2` builds `rustdoc`                              | `build/HOST/stage2-tools/HOST`                                  |
+| copy `rustdoc`                                         | `build/HOST/stage2/bin`                                         |
 
 `--stage=2` stops here.
 

src/building/how-to-build-and-run.md

@@ -95,10 +95,11 @@ The result is that compiling `rustc` is done in stages:
     particular, the stage1 compiler itself was built by stage0 and
     hence not by the source in your working directory: this means that
     the symbol names used in the compiler source may not match the
-    symbol names that would have been made by the stage1 compiler.
-    This can be important when using dynamic linking (e.g., with
-    derives). Sometimes this means that some tests don't work when run
-    with stage1.
+    symbol names that would have been made by the stage1 compiler. This is
+    important when using dynamic linking and the lack of ABI compatibility
+    between versions. This primarily manifests when tests try to link with any
+    of the `rustc_*` crates or use the (now deprecated) plugin infrastructure.
+    These tests are marked with `ignore-stage1`.
 - **Stage 2:** we rebuild our stage1 compiler with itself to produce
   the stage2 compiler (i.e. it builds itself) to have all the _latest
   optimizations_. (By default, we copy the stage1 libraries for use by