Fix compilation on win32 platform.

- Undefine NDEBUG for the lemon-generated parser, ensuring debugsymbols
  are included.
- Build the templatetokenizer, builtins and variableaccessor tests inside
  of the library. This fixes private symbols (to be tested) not being
  found.

Signed-off-by: Alexander Siol <dunklermeuchler@gmail.com>
Prepare Twig for in-source export.

Signed-off-by: Alexander Siol <dunklermeuchler@gmail.com>