Fix getdirentries(2) under 32-bit compat.

[brooks]

Summary

The latest version of getdirentries (syscall 554) takes a pointer
an an off_t as the last argument. The old version which copies out
an int32_t was being used instead. Use the standard sys_getdirentries()
implementation instead.

[kib]

Please do not put the diffs for generated files neither in review nor in the main commit.