[wasm] use -sdk instead of -Xcc --sysroot for ClangImporter

Author: kateinoigakukun

test/lit.cfg

@@ -1850,8 +1850,8 @@ elif run_os == 'wasi':
     config.target_build_swift = ' '.join([
         config.swiftc,
         '-target', config.variant_triple,
-        '-Xcc', '--sysroot=%s' % config.variant_sdk,
         '-Xclang-linker', '--sysroot=%s' % config.variant_sdk,
+        '-sdk', config.variant_sdk,
         '-toolchain-stdlib-rpath', config.resource_dir_opt, 
         mcp_opt, config.swift_test_options,
         config.swift_driver_test_options, swift_execution_tests_extra_flags])
@@ -1863,7 +1863,7 @@ elif run_os == 'wasi':
     config.target_swift_frontend = ' '.join([
         config.swift_frontend,
         '-target', config.variant_triple,
-        '-Xcc', '--sysroot=%s' % config.variant_sdk,
+        '-sdk', config.variant_sdk,
         config.resource_dir_opt, mcp_opt,
         config.swift_test_options, config.swift_frontend_test_options])
     subst_target_swift_frontend_mock_sdk = config.target_swift_frontend