[LSan][Darwin][NFC] Add comment explaining test failure

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@354290 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/sanitizer_common/TestCases/Posix/sanitizer_set_death_callback_test.cc b/test/sanitizer_common/TestCases/Posix/sanitizer_set_death_callback_test.cc
index ee8f822..9c5ae13 100644
--- a/test/sanitizer_common/TestCases/Posix/sanitizer_set_death_callback_test.cc
+++ b/test/sanitizer_common/TestCases/Posix/sanitizer_set_death_callback_test.cc
@@ -3,7 +3,7 @@
 // REQUIRES: stable-runtime
 
 // XFAIL: ubsan
-// FIXME(dliew): Make this test work on Darwin with LSan
+// FIXME: On Darwin, LSAn detects the leak, but does not invoke the death_callback.
 // XFAIL: darwin && lsan
 
 #include <sanitizer/common_interface_defs.h>