Use a normal global variable for rb_tr_cext instead of truffle_assign_managed()

Author: eregon

lib/cext/include/truffleruby/truffleruby-pre.h

@@ -48,7 +48,7 @@ typedef VALUE ID;
 // Support
 
 extern void* rb_tr_cext;
-#define RUBY_CEXT ((void *)(&rb_tr_cext))
+#define RUBY_CEXT rb_tr_cext
 
 #define MUST_INLINE __attribute__((always_inline)) inline
 

src/main/c/cext/ruby.c

@@ -87,7 +87,8 @@ static int rb_tr_fprintf_value(FILE *stream,
 // Run when loading C-extension support
 
 void rb_tr_init(void *ruby_cext) {
-  truffle_assign_managed(&rb_tr_cext, ruby_cext);
+  rb_tr_cext = ruby_cext;
+
   #ifdef __APPLE__
   printf_domain = new_printf_domain();
   register_printf_domain_function(printf_domain, 'Y', rb_tr_fprintf_value, rb_tr_fprintf_value_arginfo, NULL);