tests: robustify -w option test

* tests/count.test: Allow nanosleep to spend a bit less time than 1 second.
unwind: fix build on 32-bit architectures

Fix compilation warnings in unwind.c on 32-bit architectures.
On some architectures getuid is actually getuid32, so change the test
to use getpid instead of getuid.

* unwind.c (STACK_ENTRY_SYMBOL_FMT): Explicitly cast function_off_set
to unsigned long.
(queue_put_error): Change the 3rd argument's type to unsigned long.
* tests/stack-fcall.c (f1): Use getpid instead of getuid.
* tests/strace-k.test: Likewise.
unwind: use fopen64 instead of fopen

* unwind.c (fopen_for_input): Define to fopen64 iff
[_LARGEFILE64_SOURCE && HAVE_FOPEN64], otherwise define it to fopen.
(build_mmap_cache): Use fopen_for_input instead of fopen.
unwind: fix a bug in range updating of binary search

* unwind.c (print_stacktrace): Fix another off-by-one error in binary search.
unwind: rename function_off_set to function_offset

* unwind.c (call_action_fn, stacktrace_walk, STACK_ENTRY_SYMBOL_FMT,
print_call_cb, sprint_call_or_error, queue_put, queue_put_call):
Rename function_off_set to function_offset.