use __init_array_start to determine readonly data section;

b72e94fa used _etext and _edata to distinguish C string literals from heap allocated strings,
but using _edata, global char arrays may be considered as string literals.  to avoid the issue,
we have to use __init_array_start, which might be less portable.  you can still use _edata, by
using MRB_NO_INIT_ARRAY_START.

include/mrbconf.h

@@ -41,6 +41,10 @@
 /* if _etext and _edata available, mruby can reduce memory used by symbols */
 //#define MRB_USE_ETEXT_EDATA
 
+/* do not use __init_array_start to determine readonly data section;
+   effective only when MRB_USE_ETEXT_EDATA is defined */
+//#define MRB_NO_INIT_ARRAY_START
+
 /* turn off generational GC by default */
 //#define MRB_GC_TURN_OFF_GENERATIONAL
 

include/mruby/value.h

@@ -213,6 +213,7 @@ mrb_undef_value(void)
 
 #ifdef MRB_USE_ETEXT_EDATA
 extern char _etext[];
+#ifdef MRB_NO_INIT_ARRAY_START
 extern char _edata[];
 
 static inline mrb_bool
@@ -221,6 +222,15 @@ mrb_ro_data_p(const char *p)
   return _etext < p && p < _edata;
 }
 #else
+extern char __init_array_start[];
+
+static inline mrb_bool
+mrb_ro_data_p(const char *p)
+{
+  return _etext < p && p < (char*)&__init_array_start;
+}
+#endif
+#else
 # define mrb_ro_data_p(p) FALSE
 #endif