[LTO] Change test/tools/lto/no-bitcode.s requirement from arm to aarch64

Set the test to properly require aarch64 instead of arm. Otherwise, this test fails with LLVM_TARGETS_TO_BUILD='ARM;X86'

bin/llvm-mc: : error: unable to get target for 'arm64-apple-ios7.0.0'

Committed on behalf of @easyaspi314 (Devin)

Differential Revision: https://reviews.llvm.org/D56472

llvm-svn: 351560