Upstreaming the BridgeOS device support and the

LC_BUILD_VERSION load command handling - this
commit is a combination of patches by Adrian
Prantl and myself.  llvm::Triple::BridgeOS 
isn't defined yet, so all references to that
are currently commented out.  

Also update Xcode project file to build the 
NativePDB etc plugins.

<rdar://problem/43353615> 

llvm-svn: 344209