[libunwind] Fix failing unwind_leaffunction.pass.cpp

[leonardchan]

Summary

Calling raise seems to not allow the frame_handler to reach the main method on our aarch64 builder (we only _Z14signal_handleri and __kernel_rt_sigreturn). Using kill(getpid(), SIGSEGV) doesn't seem to have this issue.

[ldionne]

Feel free to ship this to unbreak the bots until we've found a real solution for D114385

[ldionne]

This should be made obsolete by D114818

libunwind/test/unwind_leaffunction.pass.cpp

 
 void signal_handler(int signum) {
   (void)signum;
   _Unwind_Backtrace(frame_handler, NULL);
   _Exit(-1);
 }
 
 __attribute__((noinline)) void crashing_leaf_func(void) {
-  raise(SIGSEGV);
+  kill(getpid(), SIGSEGV);
 }
 
 int main(int, char**) {
   signal(SIGSEGV, signal_handler);
   crashing_leaf_func();
   return -2;
 }