rustc-dev-guide subtree update

src/doc/rustc-dev-guide/rust-version

@@ -1 +1 @@
-4fa824bb78318a3cba8c7339d5754b4909922547
+b1b464d6f61ec8c4e609c1328106378c066a9729

src/doc/rustc-dev-guide/src/building/how-to-build-and-run.md

@@ -235,12 +235,6 @@ What this command does is:
 - Build `library` (the standard libraries) with the stage1 compiler that was just built.
 - Assemble a working stage1 sysroot, containing the stage1 compiler and stage1 standard libraries.
 
-To build `rustc` with the in-tree `std`, use this command instead:
-
-```console
-./x build library --stage 2
-```
-
 This final product (stage1 compiler + libs built using that compiler)
 is what you need to build other Rust programs (unless you use `#![no_std]` or
 `#![no_core]`).

src/doc/rustc-dev-guide/src/contributing.md

@@ -52,9 +52,9 @@ channels: stable, beta, and nightly.
 
 - **Stable**: this is the latest stable release for general usage.
 - **Beta**: this is the next release (will be stable within 6 weeks).
-- **Nightly**: follows the `master` branch of the repo. This is the only
-  channel where unstable, incomplete, or experimental features are usable with
-  feature gates.
+- **Nightly**: follows the `master` branch of the repo.
+  This is the only channel where unstable features are intended to be used,
+  which happens via opt-in feature gates.
 
 See [this chapter on implementing new features](./implementing_new_features.md) for more
 information.

src/doc/rustc-dev-guide/src/offload/usage.md

@@ -56,6 +56,13 @@ fn main() {
 unsafe extern "C" {
     pub fn kernel_1(array_b: *mut [f64; 256]);
 }
+
+#[cfg(not(target_os = "linux"))]
+#[unsafe(no_mangle)]
+#[inline(never)]
+pub extern "gpu-kernel" fn kernel_1(x: *mut [f64; 256]) {
+    unsafe { (*x)[0] = 21.0 };
+}
 ```
 
 ## Compile instructions