Fix LLVM installation: Use ARM64 version instead of x64

Scoop installs x64 LLVM on ARM64 Windows. Manually download and install
LLVM 19.1.4 ARM64 (WoA64) version from official LLVM releases.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: WebKit ARM64 Builder

.github/workflows/build.yml

@@ -264,8 +264,15 @@ jobs:
             echo "$env:USERPROFILE\scoop\shims" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
           }
           
-          # Install all tools via Scoop except Ruby
-          scoop install cmake ninja python perl llvm
+          # Install tools via Scoop (except Ruby and LLVM which need ARM64 versions)
+          scoop install cmake ninja python perl
+          
+          # Install LLVM ARM64 manually (Scoop downloads x64 on ARM64)
+          $llvmUrl = "https://github.com/llvm/llvm-project/releases/download/llvmorg-19.1.4/LLVM-19.1.4-woa64.exe"
+          $llvmExe = "$env:TEMP\llvm.exe"
+          Invoke-WebRequest -Uri $llvmUrl -OutFile $llvmExe
+          Start-Process -FilePath $llvmExe -ArgumentList "/S", "/D=C:\LLVM" -Wait
+          echo "C:\LLVM\bin" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
           
           # Install Ruby manually since Scoop's Ruby fails on ARM64
           $rubyUrl = "https://github.com/oneclick/rubyinstaller2/releases/download/RubyInstaller-3.3.6-1/rubyinstaller-devkit-3.3.6-1-x64.exe"