Add aarch64-pc-windows-msvc to CI (build only).

Build webpki on aarch64-pc-windows-msvc. Don't run it since there are no
aarch64-pc-windows-msvc runners available.

.github/workflows/ci.yml

@@ -146,6 +146,7 @@ jobs:
           # platforms mostly to smoketest that the build machinery in mk/ is
           # portable.
           - arm-unknown-linux-gnueabihf
+          - aarch64-pc-windows-msvc
           - i686-pc-windows-msvc
           - x86_64-unknown-linux-musl
           - x86_64-unknown-linux-gnu
@@ -170,6 +171,11 @@ jobs:
             rust_channel: 1.46.0
 
         include:
+          - target: aarch64-pc-windows-msvc
+            host_os: windows-latest
+            # GitHub Actions doesn't have a way to run this target yet.
+            cargo_options: --no-run
+
           - target: arm-unknown-linux-gnueabihf
             host_os: ubuntu-22.04
 
@@ -202,6 +208,11 @@ jobs:
       - if: ${{ matrix.target == 'aarch64-apple-darwin' }}
         run: echo "DEVELOPER_DIR=/Applications/Xcode_12.2.app/Contents/Developer" >> $GITHUB_ENV
 
+      - if: ${{ matrix.target == 'aarch64-pc-windows-msvc' }}
+        run: |
+          echo "C:\Program Files (x86)\Microsoft Visual Studio\2022\Enterprise\VC\Tools\Llvm\x64\bin" >> $GITHUB_PATH
+        shell: bash
+
       - if: ${{ !contains(matrix.host_os, 'windows') }}
         run: |
           mk/cargo.sh test -vv --target=${{ matrix.target }} ${{ matrix.cargo_options }} ${{ matrix.features }} ${{ matrix.mode }}

Cargo.toml

@@ -61,10 +61,13 @@ untrusted = "0.9"
 
 [dev-dependencies]
 base64 = "0.9.1"
-rcgen = { version = "0.11.3", default-features = false }
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 
+# XXX: rcgen cannot build on this target because it depends on *ring* 0.16 which doens't support it.
+[target.'cfg(not(all(target_arch = "aarch64", target_os = "windows")))'.dev-dependencies]
+rcgen = { version = "0.11.3", default-features = false }
+
 [profile.bench]
 opt-level = 3
 debug = false

src/verify_cert.rs

@@ -416,6 +416,8 @@ where
     Err(Error::UnknownIssuer.into())
 }
 
+// XXX: See comment about rcgen dev-dependency in Cargo.toml.
+#[cfg(not(all(target_arch = "aarch64", target_os = "windows")))]
 #[cfg(feature = "alloc")]
 #[cfg(test)]
 mod tests {