filter: memory leak free scanner postprocessing.

filter: memory leak free scanner postprocessing.

**Issue:**
Scanner postprocessing leaks memory during correction of `#line`
directives values and generation of C header file.

**Root cause:**
`filter_fix_linedirs` and `filter_tee_header` functions do not
dispose allocated memory.

**Solution:**
Automatically reclaim affected memory by allocating it on stack
insted of heap. Stack allocation should not be a problem as its
only 512 bytes and there is no recursive calls.