feat(linux): add --sysroot plumbing for bundled toolchains (#224)

* feat(linux): add --sysroot plumbing for bundled toolchains

* fix(linux): clear cached CMAKE_SYSROOT when --sysroot is omitted

* fix(linux): reject null/empty --sysroot in install command

Launcher/WiiCompiled.Setup.Linux/BuildRunner.cs

@@ -13,7 +13,8 @@ internal static class BuildRunner
         string workspace, string profile, string outputDir, string? baseOutputDir,
         string? retroDir, string? retroWfcOfflineDir, bool skipRetroWfcPayload,
         bool forceCleanBuild, string? translatorBin, string? ccBin, string? cxxBin, string? fuseLd,
-        string? cmakeBin, string? ninjaBin, string? nativePrebuiltDir, IInstallReporter reporter,
+        string? cmakeBin, string? ninjaBin, string? nativePrebuiltDir, string? sysroot,
+        IInstallReporter reporter,
         CancellationToken cancellationToken)
     {
         var script = Path.Combine(workspace, "Launcher", "local-build.sh");
@@ -77,6 +78,10 @@ internal static class BuildRunner
         {
             startInfo.ArgumentList.Add("--native-prebuilt-dir"); startInfo.ArgumentList.Add(nativePrebuiltDir);
         }
+        if (!string.IsNullOrEmpty(sysroot))
+        {
+            startInfo.ArgumentList.Add("--sysroot"); startInfo.ArgumentList.Add(sysroot);
+        }
 
         using var process = new Process { StartInfo = startInfo };
         var window = new BuildProgressWindow(reporter, InstallStages.Build, start: 6, end: 96);

Launcher/WiiCompiled.Setup.Linux/Program.cs

@@ -143,6 +143,15 @@ internal static class Program
             retroWfcOfflineDir = cacheDir;
         }
 
+        var sysroot = flags.GetValueOrDefault("sysroot");
+        // --sysroot explicitly provided (even as bare flag at end of argv, which ParseArgs
+        // stores as null) must carry a path; omitting --sysroot entirely is fine (local-build.sh
+        // adds -UCMAKE_SYSROOT to clear any stale cached value from a prior configure).
+        if (flags.ContainsKey("sysroot") && string.IsNullOrWhiteSpace(sysroot))
+        {
+            throw new ArgumentException("--sysroot requires a non-empty directory path.");
+        }
+
         await BuildRunner.RunAsync(
             workspace, profile, installDir, baseInstallDir,
             retroDir,
@@ -156,6 +165,7 @@ internal static class Program
             flags.GetValueOrDefault("cmake"),
             flags.GetValueOrDefault("ninja"),
             flags.GetValueOrDefault("native-prebuilt-dir"),
+            sysroot,
             reporter, token);
 
         reporter.Progress(InstallStages.Shortcuts, "Creating shortcuts", 98);
@@ -324,7 +334,7 @@ internal static class Program
                   {--download-retro-wfc-payload | --skip-retro-wfc-payload}]
                   [--force-clean-build] [--translator-bin PATH] [--disc-tool-bin PATH]
                   [--cc PATH] [--cxx PATH] [--fuse-ld NAME_OR_PATH] [--cmake PATH] [--ninja PATH]
-                  [--native-prebuilt-dir DIR] [--progress-json] [--workspace DIR]
+                  [--native-prebuilt-dir DIR] [--sysroot PATH] [--progress-json] [--workspace DIR]
           uninstall
           launch-base
           launch-retro

Launcher/local-build.sh

@@ -65,6 +65,7 @@ translator_dll_override=""
 translator_bin_override=""
 fuse_ld_override=""
 native_prebuilt_dir=""
+sysroot=""
 
 usage() {
     cat <<'EOF'
@@ -87,6 +88,8 @@ Usage: local-build.sh --output-dir DIR [options]
   --translator-bin PATH           Self-contained Translator.Cli executable (skips building AND needs no dotnet at all)
   --native-prebuilt-dir DIR       Precompiled aurora/third-party package (see Prepare-NativePrebuilt.sh);
                                    skips compiling aurora-main from source entirely
+  --sysroot PATH                   Passed to CMake as -DCMAKE_SYSROOT: where the compiler resolves
+                                   standard headers/startup files
 EOF
 }
 
@@ -110,6 +113,7 @@ while [[ $# -gt 0 ]]; do
         --translator-dll) translator_dll_override=$2; shift 2 ;;
         --translator-bin) translator_bin_override=$2; shift 2 ;;
         --native-prebuilt-dir) native_prebuilt_dir=$2; shift 2 ;;
+        --sysroot) sysroot=$2; shift 2 ;;
         -h|--help) usage; exit 0 ;;
         *) fail "unknown argument: $1" ;;
     esac
@@ -414,6 +418,14 @@ fi
 if [[ -n "$native_prebuilt_dir" ]]; then
     configure_args+=(-DMKW_NATIVE_PREBUILT_DIR="$native_prebuilt_dir")
 fi
+if [[ -n "$sysroot" ]]; then
+    configure_args+=(-DCMAKE_SYSROOT="$sysroot")
+else
+    # Explicitly clear any cached CMAKE_SYSROOT from a prior configure so an
+    # incremental build that transitions from one sysroot to none does not
+    # silently keep the stale cached path.
+    configure_args+=(-UCMAKE_SYSROOT)
+fi
 
 log_step configure-native "Configuring the native toolchain"
 "$cmake_bin" "${configure_args[@]}"