Add duk_errmsg.c for gathering shared error msgs

src/duk_errmsg.c

@@ -0,0 +1,10 @@
+/*
+ *  Shared error message strings
+ *
+ *  To minimize code footprint, try to share error messages inside Duktape
+ *  code.
+ */
+
+#include "duk_internal.h"
+
+const char *duk_errmsg_invalid_count = "invalid count";

src/duk_errmsg.h

@@ -0,0 +1,6 @@
+#ifndef DUK_ERRMSG_H_INCLUDED
+#define DUK_ERRMSG_H_INCLUDED
+
+extern const char *duk_errmsg_invalid_count;
+
+#endif  /* DUK_ERRMSG_H_INCLUDED */

src/duk_internal.h

@@ -48,6 +48,7 @@ DUK_USE_USER_DECLARE()
 #include "duk_forwdecl.h"
 #include "duk_builtins.h"  /* autogenerated: strings and built-in object init data */
 
+#include "duk_errmsg.h"
 #include "duk_js_bytecode.h"
 #include "duk_lexer.h"
 #include "duk_js_compiler.h"