rt: Set the stack depth limit to 1GB. Abort on error.

People hit the recursion depth limit too often, it's not possible
to unwind reliably from out-of-stack.

Issues #3555, #3695

src/rt/rust_env.cpp

@@ -97,7 +97,7 @@ get_max_stk_size() {
         return strtol(maxsz, NULL, 0);
     }
     else {
-        return 1024*1024*8;
+        return 1024*1024*1024;
     }
 }