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
It is otherwise impossible to determine which test failed sanitizer/valgrind
check. test/functional/helpers.lua module return was changed so that tests which
do not provide after_each function to get new check will automatically fail.
This is necessary for newer versions of Busted, otherwise assert will be
nil and the tests will die.
Note: this does not mean the tests now work with the latest Busted.
There are still several issues preventing that from happening.
