Use helper function to read 'ob_fval'.

Author: fangerer

graalpython/com.oracle.graal.python.cext/src/capi.c

@@ -714,3 +714,7 @@ int truffle_ptr_compare(void* x, void* y, int op) {
         return -1;
     }
 }
+
+double truffle_read_ob_fval(PyFloatObject* fobj) {
+	return fobj->ob_fval;
+}

graalpython/com.oracle.graal.python/src/com/oracle/graal/python/builtins/objects/cext/NativeCAPISymbols.java

@@ -52,7 +52,7 @@ public abstract class NativeCAPISymbols {
     public static final String FUN_PY_NONE_HANDLE = "PyNoneHandle";
     public static final String FUN_WHCAR_SIZE = "PyTruffle_Wchar_Size";
     public static final String FUN_PY_TRUFFLE_CSTR_TO_STRING = "PyTruffle_CstrToString";
-    public static final String FUN_PY_FLOAT_AS_DOUBLE = "PyFloat_AsDouble";
+    public static final String FUN_PY_FLOAT_AS_DOUBLE = "truffle_read_ob_fval";
     public static final String FUN_GET_OB_TYPE = "get_ob_type";
     public static final String FUN_DEREF_HANDLE = "truffle_deref_handle_for_managed";
     public static final String FUN_GET_BYTE_ARRAY_TYPE_ID = "get_byte_array_typeid";