Xfail the new test in C++03 mode (the modules build tries to include main headers, not old frozen headers)

Author: var-const

libcxx/test/libcxx/Wnon_modular_include_in_module.compile.pass.cpp

@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 // REQUIRES: target={{.*}}-apple-{{.*}}
+// XFAIL: FROZEN-CXX03-HEADERS-FIXME
 
 // This test ensures that libc++ supports being compiled with modules enabled and with
 // -Wnon-modular-include-in-module. This effectively checks that we don't include any