Correct test to target 'unknown'

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@196060 91177308-0d34-0410-b5e6-96231b3b80d8

test/Rewriter/no-integrated-preprocessing-64bit.m

-// RUN: %clang -target x86_64-unkown-unknown -fms-extensions -rewrite-objc %s -o - | FileCheck %s
+// RUN: %clang -target x86_64-unknown-unknown -fms-extensions -rewrite-objc %s -o - | FileCheck %s
 // rdar://12189793
 
 #ifdef __cplusplus