clang/test/Misc/backend-optimization-failure.cpp: Appease to add -triple=x86_64.

FIXME: Could this be made generic?

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@213441 91177308-0d34-0410-b5e6-96231b3b80d8

test/Misc/backend-optimization-failure.cpp

-// RUN: %clang_cc1 %s -O3 -emit-llvm -gline-tables-only -S -verify -o /dev/null
+// RUN: %clang_cc1 -triple x86_64-unknown-unknown %s -O3 -emit-llvm -gline-tables-only -S -verify -o /dev/null
+// REQUIRES: x86-registered-target
 
 // Test verifies optimization failures generated by the backend are handled
 // correctly by clang. LLVM tests verify all of the failure conditions.