Allocate the list for generic parameters in tstoreddef only on demand as most defs won't contain generic parameters anyway (avoids a little bit of runtime and memory overhead per def).

symdef.pas, tstoreddef:
  + comment that the list is allocated on demand (and thus should be checked for Nil)
  + fillgenericparas: create the list when adding at least one generic parameter symbol
  - create & ppuload: don't create list instance anymore
  + is_generic & is_specialization: check whether the list is assigned
defcmp.pas, compare_defs_ext:
  + check whether "genericparas" list is assigned
pgenutil.pas:
  + check_generic_constraints: check whether "genericparas" is assigned
  + insert_generic_parameter_types: create list before adding generic parameters

git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@24627 3ad0048d-3df7-0310-abae-a5850022a9f2