This test case only fails with asserts on

Fixes <rdar://problem/56196703>.

Author: slavapestov

validation-test/compiler_crashers_fixed/28723-unreachable-executed-at-swift-lib-sema-csdiag-cpp-4012.swift

@@ -6,7 +6,7 @@
 // See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
 // rdar://56144412
-// XFAIL: *
+// XFAIL: asserts
 // RUN: not %target-swift-frontend %s -emit-ir
 func t(UInt=__FUNCTION__
 func&t(