Previous commit made preprocess.lua know how its output will be used. This moves 
state to cimport, making only it know which is cleaner.

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

The primitive C canonicalizer we use to strip out duplicate header
declarations and keep luajit's ffi happy, didn't work properly in this case.

What happened is this (in /usr/include/ctype.h):

__DARWIN_CTYPE_TOP_inline int
isspecial(int _c)
{
        return (__istype(_c, _CTYPE_T));
}

Gets preprocessed to something like:

__inline int
isspecial(int _c)
{
        return (__istype(_c, _CTYPE_T));
}

On OSX/gcc. The formatter wasn't recognizing this entire function as
something to put on a single line because it naively just checks for
"static" or "inline" for that, but not "__inline".

This error doesn't occur on OSX/clang. Without looking further into it, I
guess that __DARWIN_CTYPE_TOP_inline gets defined to inline on clang, but
__inline on gcc, for some reason.

This helps issue #1572 along.

temporarily comment out call to vim_deltempdir() to avoid segfault