Fix missing comma in lit.cfg

Author: MaxDesiatov

test/lit.cfg

@@ -1383,7 +1383,7 @@ elif run_os == 'wasi':
         config.swiftc,
         '-target', config.variant_triple,
         '-Xcc', '--sysroot=%s' % config.variant_sdk,
-        '-Xclang-linker' '--sysroot=%s' % config.variant_sdk,
+        '-Xclang-linker', '--sysroot=%s' % config.variant_sdk,
         '-tools-directory', tools_directory,
         '-toolchain-stdlib-rpath', resource_dir_opt, 
         mcp_opt, config.swift_test_options,