Fix directory test on mac

runtime/bin/directory_test.cc

Index: runtime/bin/directory_test.cc
diff --git a/runtime/bin/directory_test.cc b/runtime/bin/directory_test.cc
index 245a5d19519731f94b785b4bba5f7e2ea6ca4d06..2cc4763d7b6ea5c8ea38ad23cd829361da6cd4d5 100644
--- a/runtime/bin/directory_test.cc
+++ b/runtime/bin/directory_test.cc
@@ -70,7 +70,7 @@ TEST_CASE(DirectorySetCurrent) {
   const char* new_current = dart::bin::Directory::Current();
   EXPECT_NOTNULL(new_current);
 
-  EXPECT_EQ(0, strcmp(system_temp, new_current));
+  EXPECT_NOTNULL(strstr(new_current, system_temp));
 
   EXPECT(dart::bin::Directory::SetCurrent(current));
 }