According to whether or not the compiler directive DontNeedLibraryCombinat is
set, we import an appropriate variant of the library. The variant depends on whether
the assertion DEBUG is set.
ToDo⊲11⊳ At the moment we only support the DEBUG and GMP version as
an option. Only the additional library postfixes d (for debug) and -gmp are supported
as a library variant, see Section 5.2.