[BOLT][TEST] Fix is-strip test for NFC testing

Author: aaupov

bolt/test/X86/is-strip.s

@@ -4,7 +4,7 @@
 # RUN: llvm-bolt %t -o %t.out 2>&1 | FileCheck %s -check-prefix=CHECK-NOSTRIP
 # RUN: cp %t %t.stripped
 # RUN: llvm-strip -s %t.stripped
-# RUN: not llvm-bolt %t.stripped -o %t.out 2>&1 | FileCheck %s -check-prefix=CHECK-STRIP
+# RUN: not llvm-bolt %t.stripped -o /dev/null 2>&1 | FileCheck %s -check-prefix=CHECK-STRIP
 # RUN: llvm-bolt %t.stripped -o %t.out --allow-stripped 2>&1 | FileCheck %s -check-prefix=CHECK-NOSTRIP
 
 # CHECK-NOSTRIP-NOT: BOLT-ERROR: stripped binaries are not supported.