gc.c: Double STACKFRAME_FOR_CALL_CFUNC (1024->2048)

ef64ab917e didn't fix the issue, so the
size seems not enough yet.

https://rubyci.org/logs/rubyci.s3.amazonaws.com/osx1014/ruby-master/log/20190809T114503Z.fail.html.gz

gc.c

@@ -4450,7 +4450,7 @@ stack_check(rb_execution_context_t *ec, int water_mark)
 #define stack_check(ec, water_mark) FALSE
 #endif
 
-#define STACKFRAME_FOR_CALL_CFUNC 1024
+#define STACKFRAME_FOR_CALL_CFUNC 2048
 
 MJIT_FUNC_EXPORTED int
 rb_ec_stack_check(rb_execution_context_t *ec)