update CI tarballs for LLVM 18

Also makes the windows CI scripts fetch the tarballs from the network if
not already on disk.

ci/x86_64-windows-debug.ps1

@@ -1,10 +1,20 @@
 $TARGET = "$($Env:ARCH)-windows-gnu"
-$ZIG_LLVM_CLANG_LLD_NAME = "zig+llvm+lld+clang-$TARGET-0.12.0-dev.2073+402fe565a"
+$ZIG_LLVM_CLANG_LLD_NAME = "zig+llvm+lld+clang-$TARGET-0.13.0-dev.69+c8b808826"
 $MCPU = "baseline"
-$PREFIX_PATH = "$($Env:USERPROFILE)\$ZIG_LLVM_CLANG_LLD_NAME"
+$ZIG_LLVM_CLANG_LLD_URL = "https://ziglang.org/deps/$ZIG_LLVM_CLANG_LLD_NAME.zip"
+$PREFIX_PATH = "$(Get-Location)\..\$ZIG_LLVM_CLANG_LLD_NAME"
 $ZIG = "$PREFIX_PATH\bin\zig.exe"
 $ZIG_LIB_DIR = "$(Get-Location)\lib"
 
+if (!(Test-Path "..\$ZIG_LLVM_CLANG_LLD_NAME.zip")) {
+    Write-Output "Downloading $ZIG_LLVM_CLANG_LLD_URL"
+    Invoke-WebRequest -Uri "$ZIG_LLVM_CLANG_LLD_URL" -OutFile "..\$ZIG_LLVM_CLANG_LLD_NAME.zip"
+
+    Write-Output "Extracting..."
+    Add-Type -AssemblyName System.IO.Compression.FileSystem ;
+    [System.IO.Compression.ZipFile]::ExtractToDirectory("$PWD\..\$ZIG_LLVM_CLANG_LLD_NAME.zip", "$PWD\..")
+}
+
 function CheckLastExitCode {
     if (!$?) {
         exit 1
@@ -25,6 +35,12 @@ Remove-Item -Path 'build-debug' -Recurse -Force -ErrorAction Ignore
 New-Item -Path 'build-debug' -ItemType Directory
 Set-Location -Path 'build-debug'
 
+# Override the cache directories because they won't actually help other CI runs
+# which will be testing alternate versions of zig, and ultimately would just
+# fill up space on the hard drive for no reason.
+$Env:ZIG_GLOBAL_CACHE_DIR="$(Get-Location)\zig-global-cache"
+$Env:ZIG_LOCAL_CACHE_DIR="$(Get-Location)\zig-local-cache"
+
 # CMake gives a syntax error when file paths with backward slashes are used.
 # Here, we use forward slashes only to work around this.
 & cmake .. `