debugger: pass along SDKROOT for the launch of the debugger

This is used by the debugger to locate the Swift module information for
the debugger.  Without this, we would fail to setup the Swift scratch
space in LLDB, which then results in the failure of the debugger and
subsequently the DAP.

Fixes: #250

Author: compnerd

src/debugger/launch.ts

@@ -183,13 +183,18 @@ export function createTestConfiguration(
         if (xcTestPath !== runtimePath) {
             testEnv.Path = `${xcTestPath};${testEnv.Path}`;
         }
+        const sdkroot = configuration.sdk === "" ? process.env.SDKROOT : configuration.sdk;
+        if (sdkroot === undefined) {
+            return null;
+        }
         return {
             type: "lldb",
             request: "launch",
             name: `Test ${ctx.swiftPackage.name}`,
             program: `${folder}/.build/debug/${ctx.swiftPackage.name}PackageTests.xctest`,
             cwd: folder,
             env: testEnv,
+            preRunCommands: [`settings set target.sdk-path ${sdkroot}`],
             preLaunchTask: `swift: Build All${nameSuffix}`,
         };
     } else {