Remove llvm-ar librarian path from Swift SDK built with no host toolchain included (#240)

Fixes #233

Author: xtremekforever

Sources/SwiftSDKGenerator/SwiftSDKRecipes/LinuxRecipe.swift

@@ -143,7 +143,12 @@ package struct LinuxRecipe: SwiftSDKRecipe {
     toolset.swiftCompiler = Toolset.ToolProperties(extraCLIOptions: swiftCompilerOptions)
 
     toolset.cxxCompiler = Toolset.ToolProperties(extraCLIOptions: ["-lstdc++"])
-    toolset.librarian = Toolset.ToolProperties(path: "llvm-ar")
+
+    // Don't include path to librarian if we're using the preinstalled toolchain
+    // Workaround for https://github.com/swiftlang/swift-package-manager/issues/9035
+    if self.hostSwiftSource != .preinstalled {
+      toolset.librarian = Toolset.ToolProperties(path: "llvm-ar")
+    }
   }
 
   package func applyPlatformOptions(

Tests/SwiftSDKGeneratorTests/SwiftSDKRecipes/LinuxRecipeTests.swift

@@ -116,7 +116,7 @@ final class LinuxRecipeTests: XCTestCase {
       ]
     )
     XCTAssertEqual(toolset.cxxCompiler?.extraCLIOptions, ["-lstdc++"])
-    XCTAssertEqual(toolset.librarian?.path, "llvm-ar")
+    XCTAssert(toolset.librarian == nil)
     XCTAssert(toolset.linker == nil)
   }