MC: Add support for mach-o build_version

LC_BUILD_VERSION is a new load command superseding the previously used
LC_XXX_MIN_VERSION commands. This adds an assembler directive along with
encoding/streaming support.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@320661 91177308-0d34-0410-b5e6-96231b3b80d8
13 files changed