[LTO][Legacy] Add API for passing LLVM options separately

In order to correctly pass options to LLVM, including options containing
spaces which are used as delimiters for multiple options in
lto_codegen_debug_options, add a new API:
lto_codegen_debug_options_array.

Unfortunately, tools/lto has no testing infrastructure yet, so there are
no tests associated with this patch.

Differential Revision: https://reviews.llvm.org/D70463