[cross-project-tests] REQUIRES: system-darwin in llgdb-tests/asan-deque.cpp

Some configurations of gdb pretty print std::deque and some don't. Make
this test run only on system-darwin (which uses lldb instead), otherwise
it will fail on some non-darwin machines and not others.

cross-project-tests/debuginfo-tests/llgdb-tests/asan-deque.cpp

 // RUN: %clangxx -arch x86_64 %target_itanium_abi_host_triple -O1 -g %s -o %t.out -fsanitize=address
 // RUN: %test_debuginfo %s %t.out
-// REQUIRES: !asan, compiler-rt
+// REQUIRES: !asan, compiler-rt, system-darwin
 //           Zorg configures the ASAN stage2 bots to not build the asan
 //           compiler-rt. Only run this test on non-asanified configurations.
+//           gdb is used on non-darwin; some configs pretty print std::deque,
+//           some don't.
 // UNSUPPORTED: apple-lldb-pre-1000
-// gdb is used on non-darwin systems and it doesn't pretty-print std::deque.
-// XFAIL: !system-darwin, (!system-darwin && gdb-clang-incompatibility)
-
+// XFAIL: !system-darwin && gdb-clang-incompatibility
 #include <deque>
 
 struct A {