[TSan][libdispatch] Disable test to unbreak build
This test requires the %link_libcxx_tsan substitution, which was
recently added and is not available in swift-5.1-branch.
// RUN: %clangxx_tsan %s %link_libcxx_tsan -o %t
// RUN: %run %t 2>&1 | FileCheck %s --implicit-check-not='ThreadSanitizer'
+// This test requires the %link_libcxx_tsan substitution, which was recently
+// added and is not available in swift-5.1-branch.
+// REQUIRES: link_libcxx_tsan
+
#include <dispatch/dispatch.h>
#include <memory>
