[cpu-profiler] Set SA_ONSTACK for the signal handler

This has no effect on our normal V8 builds as we don't set an
alternate stack.

Embedders like Go have to use alt stacks so this makes them work
with V8 if they have set up an alt stack themselves.

Change-Id: Icf3f4b39c026948875f5b2762ea6ffabaab03e8b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2505718Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70855}

src/libsampler/sampler.cc

@@ -329,9 +329,9 @@ class SignalHandler {
     sa.sa_sigaction = &HandleProfilerSignal;
     sigemptyset(&sa.sa_mask);
 #if V8_OS_QNX
-    sa.sa_flags = SA_SIGINFO;
+    sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
 #else
-    sa.sa_flags = SA_RESTART | SA_SIGINFO;
+    sa.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;
 #endif
     signal_handler_installed_ =
         (sigaction(SIGPROF, &sa, &old_signal_handler_) == 0);