mruby-rational/rational.c: wrap prototype with `mrb_float`
When `MRB_NO_FLOAT` is defined, `mrb_float` is not defined.
MODIFY
mrbgems/mruby-rational/src/rational.c
mrbgems/mruby-rational/src/rational.c
#include <mruby/numeric.h>
#include <mruby/presym.h>
+#ifndef MRB_NO_FLOAT
mrb_value mrb_complex_new(mrb_state *, mrb_float, mrb_float);
+#endif
mrb_bool mrb_complex_eq(mrb_state *mrb, mrb_value, mrb_value);
mrb_value mrb_complex_add(mrb_state *mrb, mrb_value, mrb_value);
mrb_value mrb_complex_sub(mrb_state *mrb, mrb_value, mrb_value);

mruby-rational/rational.c: wrap prototype with `mrb_float`

When `MRB_NO_FLOAT` is defined, `mrb_float` is not defined.