Increase STACKFRAME_FOR_CALL_CFUNC

On below env, miniruby requires 568 and ruby requires 838 to pass.
* ruby -v: ruby 2.5.0dev (2017-08-28 trunk 59670) [x86_64-freebsd10.3]
* gcc8 (FreeBSD Ports Collection) 8.0.0 20170828 (experimental)

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@59676 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 1 insertions, 1 deletions

diff --git a/gc.c b/gc.c
index 095bf75c1d..284ddaed15 100644
--- a/gc.c
+++ b/gc.c
@@ -4033,7 +4033,7 @@ stack_check(rb_thread_t *th, int water_mark)
 #define stack_check(th, water_mark) FALSE
 #endif
 
-#define STACKFRAME_FOR_CALL_CFUNC 512
+#define STACKFRAME_FOR_CALL_CFUNC 838
 
 int
 rb_threadptr_stack_check(rb_thread_t *th)