Build: quote the path string for bundle resources

We need to ensure that we escape `\` for paths in strings.  This enables
using bundles for tests on Windows.

Author: compnerd

Sources/Build/BuildPlan.swift

@@ -576,13 +576,21 @@ public final class SwiftTargetBuildDescription {
         guard let bundlePath = self.bundlePath else { return }
 
         let stream = BufferedOutputByteStream()
+
+        let mainPath: String = AbsolutePath(Bundle.main.bundlePath)
+                                  .appending(component: bundlePath.basename)
+                                  .pathString
+                                  .replacingOccurrences(of: "\\", with: "\\\\")
+        let buildPath: String =
+            bundlePath.pathString.replacingOccurrences(of: "\\", with: "\\\\")
+
         stream <<< """
         import class Foundation.Bundle
 
         extension Foundation.Bundle {
             static var module: Bundle = {
-                let mainPath = Bundle.main.bundlePath + "/" + "\(bundlePath.basename)"
-                let buildPath = "\(bundlePath.pathString)"
+                let mainPath = "\(mainPath)"
+                let buildPath = "\(buildPath)"
 
                 let preferredBundle = Bundle(path: mainPath)