PR14179: Split up loc2c-runtime.h for linux|dyninst

PR14179: Split up loc2c-runtime.h for linux|dyninst

* runtime/loc2c-runtime.h: Remove deref functions and special register
  handling from this shared base, and rename k_dwarf_register_N to
  pt_dwarf_register_N to be more neutral.
* runtime/linux/loc2c-runtime.h: Move the deref functions and special
  register handling here.  Nothing new, just transplanted.
* runtime/dyninst/loc2c-runtime.h: Add deref and register functions.
* runtime/dyninst/copy.c (__copy_from_user, __copy_to_user): Move from
  linux_def.h, since these are custom implementations, not kernel copies.
  (_stp_strncpy_from_user, _stp_copy_from_user): New implementations.