C: fix #312 -DNO_DYNAMIC_LOADING with --staticxs disables DynaLoader

--staticxs explicitly sets -DNO_DYNAMIC_LOADING which prevents DynaLoader being booted.
And then uses NO_DYNAMIC_LOADING to decide if to dynaload or boot the staticxs modules.

We need to keep the first part, always boot DynaLoader (if usedl is available),
renamed NO_DYNAMIC_LOADING to STATICXS to avoid further confusion
changed in C and perlcc.