Add 'REQUIRES: asserts' to test undef-args.ll added in #135247 to skip test when asserts are not present.

Should fix bot failure: https://lab.llvm.org/buildbot/#/builders/202/builds/601

Author: dyung

llvm/test/CodeGen/PowerPC/undef-args.ll

@@ -1,6 +1,8 @@
 ;; Tests that extending poison results in undef.
 ;; Also tests that there are redundant instructions loading 0 into argument registers for unused arguments.
 
+; REQUIRES: asserts
+
 ; RUN: llc -verify-machineinstrs -mtriple powerpc-ibm-aix-xcoff -debug-only=isel \
 ; RUN:   %s -o - 2>&1 | FileCheck --check-prefix=CHECKISEL32 %s