Rollup merge of #126039 - dpaoliello:arm64ecbuild, r=davidtwco

Promote `arm64ec-pc-windows-msvc` to tier 2

MCP: <https://github.com/rust-lang/compiler-team/issues/746>

* Update platform support docs
* Add `arm64ec-pc-windows-msvc` as a target to the existing AArch64 Windows build in CI.
* Fix docs build break.
* Add `arm64ec-pc-windows-msvc` to build manifest.

CI build (succeeded, but upload to S3 failed): <https://github.com/rust-lang/rust/actions/runs/9388227822/job/25853013083?pr=126039>

library/std/src/os/linux/raw.rs

@@ -244,7 +244,11 @@ mod arch {
     pub use libc::{blkcnt_t, blksize_t, ino_t, nlink_t, off_t, stat, time_t};
 }
 
-#[cfg(target_arch = "aarch64")]
+#[cfg(any(
+    target_arch = "aarch64",
+    // Arm64EC is Windows-only, but docs are always build as Linux, so re-use AArch64 for Arm64EC.
+    all(doc, target_arch = "arm64ec")
+))]
 mod arch {
     use crate::os::raw::{c_int, c_long};
 

src/ci/github-actions/jobs.yml

@@ -428,6 +428,7 @@ auto:
       RUST_CONFIGURE_ARGS: >-
         --build=x86_64-pc-windows-msvc
         --host=aarch64-pc-windows-msvc
+        --target=aarch64-pc-windows-msvc,arm64ec-pc-windows-msvc
         --enable-full-tools
         --enable-profiler
       SCRIPT: python x.py dist bootstrap --include-default-paths

src/doc/rustc/src/platform-support.md

@@ -146,6 +146,7 @@ target | std | notes
 [`arm-linux-androideabi`](platform-support/android.md) | ✓ | Armv6 Android
 `arm-unknown-linux-musleabi` | ✓ | Armv6 Linux with musl 1.2.3
 `arm-unknown-linux-musleabihf` | ✓ | Armv6 Linux with musl 1.2.3, hardfloat
+[`arm64ec-pc-windows-msvc`](platform-support/arm64ec-pc-windows-msvc.md) | ✓ | Arm64EC Windows MSVC
 [`armebv7r-none-eabi`](platform-support/armv7r-none-eabi.md) | * | Bare Armv7-R, Big Endian
 [`armebv7r-none-eabihf`](platform-support/armv7r-none-eabi.md) | * | Bare Armv7-R, Big Endian, hardfloat
 `armv5te-unknown-linux-gnueabi` | ✓ | Armv5TE Linux (kernel 4.4, glibc 2.23)
@@ -240,7 +241,6 @@ target | std | host | notes
 -------|:---:|:----:|-------
 [`arm64e-apple-ios`](platform-support/arm64e-apple-ios.md) | ✓ | | ARM64e Apple iOS
 [`arm64e-apple-darwin`](platform-support/arm64e-apple-darwin.md)  | ✓ | ✓ | ARM64e Apple Darwin
-[`arm64ec-pc-windows-msvc`](platform-support/arm64ec-pc-windows-msvc.md) | ? | | Arm64EC Windows MSVC
 [`aarch64-apple-ios-macabi`](platform-support/apple-ios-macabi.md) | ✓ |  | Apple Catalyst on ARM64
 [`aarch64-apple-tvos`](platform-support/apple-tvos.md) | ✓ |  | ARM64 tvOS
 [`aarch64-apple-tvos-sim`](platform-support/apple-tvos.md) | ✓ |  | ARM64 tvOS Simulator

src/doc/rustc/src/platform-support/arm64ec-pc-windows-msvc.md

@@ -1,6 +1,6 @@
 # `arm64ec-pc-windows-msvc`
 
-**Tier: 3**
+**Tier: 2**
 
 Arm64EC ("Emulation Compatible") for mixed architecture (AArch64 and x86_64)
 applications on AArch64 Windows 11. See <https://learn.microsoft.com/en-us/windows/arm/arm64ec>.
@@ -21,6 +21,9 @@ Only supported backend is LLVM 18 or above:
 * 18.1.4 fixed linking issue for some intrinsics implemented in
   `compiler_builtins`.
 
+Visual Studio 2022 (or above) with the "ARM64/ARM64EC built tools" component and
+the Windows 11 SDK are required.
+
 ### Reusing code from other architectures - x86_64 or AArch64?
 
 Arm64EC uses `arm64ec` as its `target_arch`, but it is possible to reuse
@@ -62,10 +65,8 @@ target = [ "arm64ec-pc-windows-msvc" ]
 
 ## Building Rust programs
 
-Rust does not yet ship pre-compiled artifacts for this target. To compile for
-this target, you will either need to build Rust with the target enabled (see
-"Building the target" above), or build your own copy using `build-std` or
-similar.
+These targets are distributed through `rustup`, and otherwise require no
+special configuration.
 
 ## Testing
 

src/tools/build-manifest/src/main.rs

@@ -71,6 +71,7 @@ static TARGETS: &[&str] = &[
     "arm-unknown-linux-gnueabihf",
     "arm-unknown-linux-musleabi",
     "arm-unknown-linux-musleabihf",
+    "arm64ec-pc-windows-msvc",
     "armv5te-unknown-linux-gnueabi",
     "armv5te-unknown-linux-musleabi",
     "armv7-linux-androideabi",