[lit] Temporarily disable shtest-timeout.py on darwin

Disabled until fixed in order to avoid random failures on green dragon.

rdar://problem/38774530

llvm-svn: 328598
diff --git a/llvm/utils/lit/tests/shtest-timeout.py b/llvm/utils/lit/tests/shtest-timeout.py
index 8798500..f9e3acc 100644
--- a/llvm/utils/lit/tests/shtest-timeout.py
+++ b/llvm/utils/lit/tests/shtest-timeout.py
@@ -1,5 +1,8 @@
 # REQUIRES: python-psutil
-
+#
+# rdar://problem/38774530
+# UNSUPPORTED: darwin
+#
 # PR33944
 # XFAIL: windows