fix build on vs2013-vs2015

include/mruby/compile.h

@@ -163,6 +163,7 @@ struct mrb_parser_state {
 MRB_API struct mrb_parser_state* mrb_parser_new(mrb_state*);
 MRB_API void mrb_parser_free(struct mrb_parser_state*);
 MRB_API void mrb_parser_parse(struct mrb_parser_state*,mrbc_context*);
+MRB_API double mrb_float_read(const char*, char**);
 
 MRB_API void mrb_parser_set_filename(struct mrb_parser_state*, char const*);
 MRB_API char const* mrb_parser_get_filename(struct mrb_parser_state*, uint16_t idx);

src/numeric.c

@@ -357,7 +357,11 @@ flo_shift(mrb_state *mrb, mrb_value x, mrb_int width)
     while (width++) {
       val /= 2;
     }
+#if defined(_ISOC99_SOURCE)
     val = trunc(val);
+#else
+    val = val > 0 ? floor(val) : ceil(val);
+#endif
     if (val == 0 && mrb_float(x) < 0) {
       return mrb_fixnum_value(-1);
     }