Pass --enable-test-discovery to swift-build to allow running test on Linux

Author: kitasuke

build-script.py

@@ -161,8 +161,11 @@ def get_installed_dylib_name():
 def get_swiftpm_invocation(toolchain, action, build_dir, release):
     swift_exec = os.path.join(toolchain, 'usr', 'bin', 'swift')
 
-    swiftpm_call = [swift_exec, action]
-    swiftpm_call.extend(['--package-path', PACKAGE_DIR])
+    swiftpm_call = [
+      swift_exec, action,
+      '--package-path', PACKAGE_DIR,
+      '--enable-test-discovery'
+    ]
     if release:
         swiftpm_call.extend(['--configuration', 'release'])
     if build_dir: