Use platform-dependent new-line character in RetraceCommandLineTests

Change-Id: I723f2c420af24ef5a51556dcbe37c28dd89c1d7c
diff --git a/src/test/java/com/android/tools/r8/retrace/RetraceCommandLineTests.java b/src/test/java/com/android/tools/r8/retrace/RetraceCommandLineTests.java
index ebe1bbf..102f7f0 100644
--- a/src/test/java/com/android/tools/r8/retrace/RetraceCommandLineTests.java
+++ b/src/test/java/com/android/tools/r8/retrace/RetraceCommandLineTests.java
@@ -65,7 +65,7 @@
         stackTrace.mapping(),
         StringUtils.joinLines(stackTrace.obfuscatedStackTrace()),
         false,
-        StringUtils.joinLines(stackTrace.retracedStackTrace()) + "\n",
+        StringUtils.joinLines(stackTrace.retracedStackTrace()) + StringUtils.LINE_SEPARATOR,
         "--verbose");
   }
 
@@ -76,7 +76,7 @@
         stackTrace.mapping(),
         StringUtils.joinLines(stackTrace.obfuscatedStackTrace()),
         false,
-        StringUtils.joinLines(stackTrace.retracedStackTrace()) + "\n",
+        StringUtils.joinLines(stackTrace.retracedStackTrace()) + StringUtils.LINE_SEPARATOR,
         "--regex=" + DEFAULT_REGULAR_EXPRESSION);
   }
 
@@ -87,7 +87,7 @@
         stackTrace.mapping(),
         StringUtils.joinLines(stackTrace.obfuscatedStackTrace()),
         false,
-        StringUtils.joinLines(stackTrace.retracedStackTrace()) + "\n",
+        StringUtils.joinLines(stackTrace.retracedStackTrace()) + StringUtils.LINE_SEPARATOR,
         "--regex=" + DEFAULT_REGULAR_EXPRESSION,
         "--info");
   }