Keeps arguments separated and not joined as a single string as long as possible.
Abstracts away additional arguments so that Gcc:preprocess should work for
compilers with different conventions should they be supported.
Works by saving all preprocessor defines and reusing them on each run. This also
saves NVIM_HEADER_H defines. Saving other defines is needed for defines like
`Map(foo, bar)` which are sometimes used to declare types or functions. Saving
types or function declarations is not needed because they are recorded as luajit
state.
Fixes#5857
