Adds a GitHub Actions CI build for aarch64-pc-windows-msvc via cross-compilation on an x86_64 host.

This promotes aarch64-pc-windows-msvc from a Tier 2 Compilation Target (std) to a Tier 2 Development Platform (std+rustc+cargo+tools).

Fixes #72881

.github/workflows/ci.yml

@@ -473,7 +473,7 @@ jobs:
             os: windows-latest-xl
           - name: dist-x86_64-msvc
             env:
-              RUST_CONFIGURE_ARGS: "--build=x86_64-pc-windows-msvc --host=x86_64-pc-windows-msvc --target=x86_64-pc-windows-msvc,aarch64-pc-windows-msvc --enable-full-tools --enable-profiler"
+              RUST_CONFIGURE_ARGS: "--build=x86_64-pc-windows-msvc --host=x86_64-pc-windows-msvc --target=x86_64-pc-windows-msvc --enable-full-tools --enable-profiler"
               SCRIPT: python x.py dist
               DIST_REQUIRE_ALL_TOOLS: 1
             os: windows-latest-xl
@@ -483,6 +483,12 @@ jobs:
               SCRIPT: python x.py dist
               DIST_REQUIRE_ALL_TOOLS: 1
             os: windows-latest-xl
+          - name: dist-aarch64-msvc
+            env:
+              RUST_CONFIGURE_ARGS: "--build=x86_64-pc-windows-msvc --host=aarch64-pc-windows-msvc --enable-full-tools --enable-profiler"
+              SCRIPT: python x.py dist
+              DIST_REQUIRE_ALL_TOOLS: 0
+            os: windows-latest-xl
           - name: dist-i686-mingw
             env:
               RUST_CONFIGURE_ARGS: "--build=i686-pc-windows-gnu --enable-full-tools --enable-profiler"

src/ci/github-actions/ci.yml

@@ -576,7 +576,7 @@ jobs:
               RUST_CONFIGURE_ARGS: >-
                 --build=x86_64-pc-windows-msvc
                 --host=x86_64-pc-windows-msvc
-                --target=x86_64-pc-windows-msvc,aarch64-pc-windows-msvc
+                --target=x86_64-pc-windows-msvc
                 --enable-full-tools
                 --enable-profiler
               SCRIPT: python x.py dist
@@ -595,6 +595,18 @@ jobs:
               DIST_REQUIRE_ALL_TOOLS: 1
             <<: *job-windows-xl
 
+          - name: dist-aarch64-msvc
+            env:
+              RUST_CONFIGURE_ARGS: >-
+                --build=x86_64-pc-windows-msvc
+                --host=aarch64-pc-windows-msvc
+                --enable-full-tools
+                --enable-profiler
+              SCRIPT: python x.py dist
+              # RLS does not build for aarch64-pc-windows-msvc. See rust-lang/rls#1693
+              DIST_REQUIRE_ALL_TOOLS: 0
+            <<: *job-windows-xl
+
           - name: dist-i686-mingw
             env:
               RUST_CONFIGURE_ARGS: --build=i686-pc-windows-gnu --enable-full-tools --enable-profiler

src/ci/scripts/install-mingw.sh

@@ -42,6 +42,13 @@ if isWindows; then
             arch=x86_64
             mingw_archive="${MINGW_ARCHIVE_64}"
             ;;
+        *aarch64*)
+            # aarch64 is a cross-compiled target. Use the x86_64
+            # mingw, since that's the host architecture.
+            bits=64
+            arch=x86_64
+            mingw_archive="${MINGW_ARCHIVE_64}"
+            ;;
         *)
             echo "src/ci/scripts/install-mingw.sh can't detect the builder's architecture"
             echo "please tweak it to recognize the builder named '${CI_JOB_NAME}'"

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

@@ -60,7 +60,7 @@ target | std | host | notes
 `aarch64-apple-ios` | ✓[^apple] |  | ARM64 iOS
 `aarch64-fuchsia` | ✓ |  | ARM64 Fuchsia
 `aarch64-linux-android` | ✓ |  | ARM64 Android
-`aarch64-pc-windows-msvc` | ✓ |  | ARM64 Windows MSVC
+`aarch64-pc-windows-msvc` | ✓ | ✓ | ARM64 Windows MSVC
 `aarch64-unknown-linux-gnu` | ✓ | ✓ | ARM64 Linux (kernel 4.2, glibc 2.17)
 `aarch64-unknown-linux-musl` | ✓ | ✓ | ARM64 Linux with MUSL
 `aarch64-unknown-none` | * |  | Bare ARM64, hardfloat