Fix unresolved symbol in standalone debug build.

Author: vchigrin

system/lib/standalone/standalone.c

@@ -25,6 +25,7 @@
 
 #include "lock.h"
 #include "emscripten_internal.h"
+#include "unwind.h"
 
 /*
  * WASI support code. These are compiled with the program, and call out
@@ -308,3 +309,7 @@ weak void _emscripten_get_progname(char* buf, int length) {
 }
 
 weak void _emscripten_runtime_keepalive_clear() {}
+
+void __throw_exception_with_stack_trace(_Unwind_Exception* exception_object) {
+  _Unwind_RaiseException(exception_object);
+}