Add --enable-test-discovery option for test command

Author: kitasuke

build-script.py

@@ -168,6 +168,9 @@ def get_swiftpm_invocation(spm_exec, build_dir, parser_header_dir,
         swiftpm_call = ['swift', 'build']
     elif spm_exec == 'swift test':
         swiftpm_call = ['swift', 'test']
+
+        # To discover test files for Linux
+        swiftpm_call.extend(['--enable-test-discovery'])
     else:
         swiftpm_call = [spm_exec]