add extern "C" guards; close #126

include/mruby/numeric.h

@@ -7,6 +7,10 @@
 #ifndef MRUBY_NUMERIC_H
 #define MRUBY_NUMERIC_H
 
+#if defined(__cplusplus)
+extern "C" {
+#endif
+
 #include <limits.h>
 
 #define RSHIFT(x,y) ((x)>>(int)(y))
@@ -18,4 +22,8 @@ mrb_value mrb_flt2big(mrb_state *mrb, mrb_float d);
 void mrb_num_zerodiv(mrb_state *mrb);
 mrb_value mrb_fix2str(mrb_state *mrb, mrb_value x, int base);
 
+#if defined(__cplusplus)
+}  /* extern "C" { */
+#endif
+
 #endif  /* MRUBY_NUMERIC_H */