unwind: fix build on 32-bit architectures

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.