SafeStack: Disable Darwin support

SafeStack support for Darwin has not been functional and was disabled in
r339719/r339720. Disable Darwin for the safestack debuginfo test.

llvm-svn: 339732

debuginfo-tests/safestack.c

@@ -1,5 +1,6 @@
 // RUN: %clang %target_itanium_abi_host_triple -arch x86_64 %s -o %t.out -g -fsanitize=safe-stack
 // RUN: %test_debuginfo %s %t.out
+// UNSUPPORTED: system-darwin
 // REQUIRES: not_asan
 //           Zorg configures the ASAN stage2 bots to not build the
 //           safestack compiler-rt.  Only run this test on