[Test] Fix a test for Windows

Author: DougGregor

test/Driver/parseable_output_unicode.swift

@@ -69,7 +69,7 @@
 // CHECK-NEXT: {
 // CHECK-NEXT:   "kind": "began",
 // CHECK-NEXT:   "name": "merge-module",
-// CHECK-NEXT:   "command": "{{.*[\\/]}}swift-frontend{{(-frontend|c)?(\.exe)?(\\")?}} -frontend -merge-modules -emit-module {{.*[\\/]}}你好-[[OUTPUT]].swiftmodule{{(\\")?}} {{.*}} -o {{.*[\\/]}}parseable_output_unicode.swift.tmp.swiftmodule{{(\\")?}}",
+// CHECK-NEXT:   "command": "{{.*[\\/]}}swift{{(-frontend|c)?(\.exe)?(\\")?}} -frontend -merge-modules -emit-module {{.*[\\/]}}你好-[[OUTPUT]].swiftmodule{{(\\")?}} {{.*}} -o {{.*[\\/]}}parseable_output_unicode.swift.tmp.swiftmodule{{(\\")?}}",
 // CHECK-NEXT:   "command_executable": "{{.*[\\/]}}swift{{(-frontend|c)?(\.exe)?(\\")?}}",
 // CHECK-NEXT:   "command_arguments": [
 // CHECK-NEXT:     "-frontend",