[dsymutil] Copy the LC_BUILD_VERSION load command into the companion binary.

LC_BUILD_VERSION contains platform information that is useful for LLDB
to match up dSYM bundles with binaries. This patch copies the load
command over into the dSYM.

rdar://problem/44145175
rdar://problem/45883463

Differential Revision: https://reviews.llvm.org/D54233

llvm-svn: 346412