Rename 'struct LLVMTargetMachine' to 'struct LLVMOpaqueTargetMachine'. 
This avoids namespace collisions with llvm::LLVMTargetMachine.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180891 91177308-0d34-0410-b5e6-96231b3b80d8