Set explicit Cargo linker in MSVC setup action

.github/actions/setup-msvc-env/action.yml

@@ -70,6 +70,7 @@ runs:
         )
 
         $envLines = & cmd.exe /c ('"{0}" -no_logo -arch={1} -host_arch={2} >nul && set' -f $vsDevCmd, $targetArch, $hostArch)
+        $vcToolsInstallDir = $null
         foreach ($line in $envLines) {
           if ($line -notmatch "^(.*?)=(.*)$") {
             continue
@@ -81,6 +82,21 @@ runs:
             if ($name -ieq "Path") {
               $name = "PATH"
             }
+            if ($name -eq "VCToolsInstallDir") {
+              $vcToolsInstallDir = $value
+            }
             "$name=$value" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append
           }
         }
+
+        if (-not $vcToolsInstallDir) {
+          throw "VCToolsInstallDir was not exported by VsDevCmd.bat"
+        }
+
+        $linker = Join-Path $vcToolsInstallDir "bin\Host${hostArch}\${targetArch}\link.exe"
+        if (-not (Test-Path $linker)) {
+          throw "MSVC linker not found at $linker"
+        }
+
+        $cargoTarget = "${{ inputs.target }}".ToUpperInvariant().Replace("-", "_")
+        "CARGO_TARGET_${cargoTarget}_LINKER=$linker" | Out-File -FilePath $env:GITHUB_ENV -Encoding utf8 -Append