Mark test as requiring x86 backend.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@143427 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/debug-info-iv.c

 // RUN: %clang_cc1 -triple x86_64-apple-darwin -Os -S -g  -o - %s | FileCheck %s
+// REQUIRES: x86-registered-target
 
 int calculate(int);
 static void test_indvars(int *Array1, int Array2[100][200]) {