Fixed test case error which caused the default cpu is changed from generic to ppc64 for triple powerpc64 (#114828)

[Summary]
Fixed test case error in the
https://lab.llvm.org/buildbot/#/builders/33/builds/5801 which
  caused by the commit #113943

Author: diggerlin

llvm/test/CodeGen/PowerPC/stack-guard-global.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
-; RUN: llc -mtriple=powerpc64 -verify-machineinstrs < %s \
+; RUN: llc -mcpu=ppc -mtriple=powerpc64 -verify-machineinstrs < %s \
 ; RUN:     | FileCheck %s --check-prefixes=BE64
 ; RUN: llc -mtriple=powerpc64le -verify-machineinstrs < %s \
 ; RUN:     | FileCheck %s --check-prefixes=LE64

llvm/test/CodeGen/PowerPC/stack-guard-tls.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
-; RUN: llc -mtriple=powerpc64 -verify-machineinstrs < %s \
+; RUN: llc -mcpu=ppc -mtriple=powerpc64 -verify-machineinstrs < %s \
 ; RUN:     | FileCheck %s --check-prefixes=BE64
 ; RUN: llc -mtriple=powerpc64le -verify-machineinstrs < %s \
 ; RUN:     | FileCheck %s --check-prefixes=LE64

llvm/test/CodeGen/PowerPC/uaddo-64.ll

@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
-; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu | FileCheck %s
+; RUN: llc < %s -mcpu=ppc -mtriple=powerpc64-unknown-linux-gnu | FileCheck %s
 ; RUN: llc < %s -mtriple=powerpc64-ibm-aix-xcoff | FileCheck %s
 
 define noundef i64 @add(i64 noundef %a, i64 noundef %b, ptr nocapture noundef writeonly %ovf) {