numeric.c: restore `fmt` argument for backward compatibility.

`mrb_float_to_str()` used to take `fmt` argument. We thought no one used
the function, and OK to remove the argument. But at least `mruby-redis`
gem used the function.

include/mruby/numeric.h

@@ -166,7 +166,7 @@ MRB_API mrb_float mrb_as_float(mrb_state *mrb, mrb_value x);
 
 /* internal functions */
 mrb_float mrb_div_float(mrb_float x, mrb_float y);
-mrb_value mrb_float_to_str(mrb_state *mrb, mrb_value x);
+mrb_value mrb_float_to_str(mrb_state *mrb, mrb_value x, const char *fmt);
 int mrb_format_float(mrb_float f, char *buf, size_t buf_size, char fmt, int prec, char sign);
 
 /* obsolete functions; will be removed */

src/numeric.c

@@ -277,8 +277,9 @@ flo_div(mrb_state *mrb, mrb_value x)
   return mrb_float_value(mrb, a);
 }
 
-MRB_API mrb_value
-mrb_float_to_str(mrb_state *mrb, mrb_value flo)
+/* the argument `fmt` is no longer used; you can pass `NULL` */
+mrb_value
+mrb_float_to_str(mrb_state *mrb, mrb_value flo, const char *fmt)
 {
   char buf[25];
 #ifdef MRB_USE_FLOAT32
@@ -330,7 +331,7 @@ flo_to_s(mrb_state *mrb, mrb_value flt)
     str = mrb_str_new_lit(mrb, "NaN");
   }
   else {
-    str = mrb_float_to_str(mrb, flt);
+    str = mrb_float_to_str(mrb, flt, NULL);
   }
 
   RSTR_SET_ASCII_FLAG(mrb_str_ptr(str));