[Sanitizer][Darwin] atos does not show line numbers for globals

atos does not show line numbers for globals and will probably not
support this anytime soon.  Mark test UNSUPPORTED instead of XFAIL.

Author: Julian Lettner

compiler-rt/test/asan/TestCases/global-location.cpp

@@ -7,8 +7,8 @@
 // COFF doesn't support debuginfo for globals. For the non-debuginfo tests, see global-location-nodebug.cpp.
 // XFAIL: windows-msvc
 
-// atos currently doesn't show source line numbers for global variables.
-// XFAIL: darwin
+// atos doesn't show source line numbers for global variables.
+// UNSUPPORTED: darwin
 
 // CHECK: AddressSanitizer: global-buffer-overflow