[clang][test] Specify triple in test/CodeGen/issue155126.c

Differences in llvm ir output break builders, e.g.
https://lab.llvm.org/buildbot/#/builders/190/builds/26289

Author: tbaederr

clang/test/CodeGen/issue155126.c

@@ -1,6 +1,6 @@
 // NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 5
-// RUN: %clang_cc1 -std=c23 %s -emit-llvm -o - | FileCheck %s
-// RUN: %clang_cc1 -std=c23 %s -emit-llvm -o - -fexperimental-new-constant-interpreter | FileCheck %s
+// RUN: %clang_cc1 -std=c23 %s -triple x86_64 -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -std=c23 %s -triple x86_64 -emit-llvm -o - -fexperimental-new-constant-interpreter | FileCheck %s
 
 enum e : bool { b = true };
 // CHECK-LABEL: define dso_local void @foo(