sigsegv_handler: handle case when it is called on original stack

If sigsegv_handler is called on original stack (for example, if segmentation
fault occurs in native application's thread that hasn't alternate signal stack)
we should call common_signal_handler directly othersize sigsegv_handler's
stackframe will be corrupted.

Author: Konstantin Baladurin

src/pal/src/exception/signal.cpp

@@ -487,8 +487,18 @@ static void sigsegv_handler(int code, siginfo_t *siginfo, void *context)
         if (contextInitialization)
         {
             contextInitialization = false;
-            ExecuteHandlerOnOriginalStack(code, siginfo, context, &returnPoint);
-            _ASSERTE(FALSE); // The ExecuteHandlerOnOriginalStack should never return
+            if (GetCurrentPalThread())
+            {
+                ExecuteHandlerOnOriginalStack(code, siginfo, context, &returnPoint);
+                _ASSERTE(FALSE); // The ExecuteHandlerOnOriginalStack should never return
+            }
+            else
+            {
+                // If thread isn't created by coreclr and has alternate signal stack GetCurrentPalThread() will return NULL too.
+                // But since in this case we don't handle hardware exceptions (IsSafeToHandleHardwareException returns false)
+                // we can call common_signal_handler on the alternate stack.
+                returnPoint.returnFromHandler = common_signal_handler(code, siginfo, context, 2, (size_t)0, (size_t)siginfo->si_addr);
+            }
         }
 
         if (returnPoint.returnFromHandler)