[ms-inline-asm] Leave alignment in bytes if the native assembler uses bytes

[ms-inline-asm] Leave alignment in bytes if the native assembler uses bytes

The existing behavior was correct on Darwin, which is probably the
platform it was written for.

Before this change, we would rewrite "align 8" to ".align 3" and then
fail to make it through the integrated assembler because 3 is not a
power of 2.

Differential Revision: http://reviews.llvm.org/D14120

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@251418 91177308-0d34-0410-b5e6-96231b3b80d8