Fix /MT flags and LLVM ARM64 installer hanging

- Remove /MT and /MTd from CMAKE_C/CXX_FLAGS (runtime library is
  controlled by CMAKE_MSVC_RUNTIME_LIBRARY)
- Extract LLVM ARM64 with 7zip instead of running installer which
  hangs forever in CI

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

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

Author: WebKit ARM64 Builder

.github/workflows/build.yml

@@ -326,12 +326,15 @@ jobs:
             scoop install perl
             scoop install make
             
-            # LLVM ARM64 has pre_install script issues in Scoop, install manually
-            Write-Host "Installing LLVM ARM64 manually..."
+            # LLVM ARM64: Download and extract manually instead of using installer
+            Write-Host "Downloading LLVM ARM64..."
             $llvmUrl = "https://github.com/llvm/llvm-project/releases/download/llvmorg-19.1.4/LLVM-19.1.4-woa64.exe"
-            $llvmExe = "$env:TEMP\llvm-installer.exe"
+            $llvmExe = "$env:TEMP\llvm.exe"
             Invoke-WebRequest -Uri $llvmUrl -OutFile $llvmExe
-            Start-Process -FilePath $llvmExe -ArgumentList "/S", "/D=C:\LLVM" -Wait
+            
+            # Extract using 7zip instead of running installer (which hangs)
+            Write-Host "Extracting LLVM ARM64..."
+            & "C:\Program Files\7-Zip\7z.exe" x $llvmExe -o"C:\LLVM" -y
             echo "C:\LLVM\bin" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
           } else {
             # Use x64 packages

windows-release.ps1

@@ -292,10 +292,10 @@ cmake -S . -B $WebKitBuild `
     "-DRuby_EXECUTABLE=${RubyPath}" `
     "-DCMAKE_C_COMPILER=clang-cl" `
     "-DCMAKE_CXX_COMPILER=clang-cl" `
-    "-DCMAKE_C_FLAGS_RELEASE=/Zi /O2 /Ob2 /DNDEBUG /MT -clang:-fno-asynchronous-unwind-tables " `
-    "-DCMAKE_CXX_FLAGS_RELEASE=/Zi /O2 /Ob2 /DNDEBUG /MT -Xclang -fno-c++-static-destructors -clang:-fno-asynchronous-unwind-tables " `
-    "-DCMAKE_C_FLAGS_DEBUG=/Zi /FS /O0 /Ob0 /MTd " `
-    "-DCMAKE_CXX_FLAGS_DEBUG=/Zi /FS /O0 /Ob0 /MTd -Xclang -fno-c++-static-destructors " `
+    "-DCMAKE_C_FLAGS_RELEASE=/Zi /O2 /Ob2 /DNDEBUG -clang:-fno-asynchronous-unwind-tables " `
+    "-DCMAKE_CXX_FLAGS_RELEASE=/Zi /O2 /Ob2 /DNDEBUG -Xclang -fno-c++-static-destructors -clang:-fno-asynchronous-unwind-tables " `
+    "-DCMAKE_C_FLAGS_DEBUG=/Zi /FS /O0 /Ob0 " `
+    "-DCMAKE_CXX_FLAGS_DEBUG=/Zi /FS /O0 /Ob0 -Xclang -fno-c++-static-destructors " `
     -DENABLE_REMOTE_INSPECTOR=ON `
     "-DCMAKE_MSVC_RUNTIME_LIBRARY=${CmakeMsvcRuntimeLibrary}" `
     @VcpkgToolchain `