Add REQUIRES: asserts to simplify_cfg_checkcast.sil

Fixes rdar://101539203: Unknown command line argument
'-debug-only=sil-simplify-cfg'

Author: atrick

test/SILOptimizer/simplify_cfg_checkcast.sil

@@ -1,5 +1,7 @@
 // RUN: %target-sil-opt -enable-sil-verify-all %s -jumpthread-simplify-cfg -enable-ossa-simplify-cfg -enable-ossa-rewriteterminator | %FileCheck %s
 // RUN: %target-sil-opt -enable-sil-verify-all %s -jumpthread-simplify-cfg -enable-ossa-simplify-cfg -enable-ossa-rewriteterminator -debug-only=sil-simplify-cfg 2>&1 | %FileCheck %s --check-prefix=CHECK-TRACE
+//
+// REQUIRES: asserts
 
 // FIXME: which of these tests actually require -jumpthread-simplify-cfg instead of -simplify-cfg?