Expose LLVMCreateTargetMachineData as data_layout.

As r263530 did for go. From that commit: "LLVMGetTargetDataLayout was
removed from the C API, and then TargetMachine.TargetData was removed.
Later, LLVMCreateTargetMachineData was added to the C API"

Differential Revision: http://reviews.llvm.org/D18677

llvm-svn: 265115