expose get_opt_constant_folding in public API

include/libfirm/irflag.h

@@ -70,6 +70,8 @@ FIRM_API int get_optimize(void);
  * Default: opt_constant_folding == 1.
  */
 FIRM_API void set_opt_constant_folding(int value);
+/** returns 0 if constant_folding is disabled, !=0 otherwise */
+FIRM_API int get_opt_constant_folding(void);
 
 /** Enables/Disables algebraic simplifications.
  *

ir/ir/irflag_t.def

@@ -43,7 +43,7 @@ E_FLAG(cse                                , 1, ON)
 I_FLAG(global_cse                         , 2, OFF)
 
 /** Evaluate operations. */
-I_FLAG(constant_folding                   , 3, ON)
+E_FLAG(constant_folding                   , 3, ON)
 
 /** Algebraic simplifications. */
 I_FLAG(algebraic_simplification           , 4, ON)