aarch64: Fix __sigset build issue on muslC
Described in issue   Taken from Alpine Linux project.
Change __sigset_t to sigset_t
@@ -202,7 +202,7 @@ typedef struct
unsigned long uc_flags;
struct ucontext *uc_link;
stack_t uc_stack;
- __sigset_t uc_sigmask;
+ sigset_t uc_sigmask;
struct unw_sigcontext uc_mcontext;
} unw_tdep_context_t;
