constify parser input strings

include/mruby/compile.h

@@ -95,8 +95,8 @@ struct mrb_parser_state* mrb_parse_nstring(mrb_state*,const char*,int);
 int mrb_generate_code(mrb_state*, mrb_ast_node*);
 
 int mrb_compile_file(mrb_state*,FILE*);
-int mrb_compile_string(mrb_state*,char*);
-int mrb_compile_nstring(mrb_state*,char*,int);
+int mrb_compile_string(mrb_state*,const char*);
+int mrb_compile_nstring(mrb_state*,const char*,int);
 
 #if defined(__cplusplus)
 }  /* extern "C" { */

src/parse.y

@@ -4812,7 +4812,7 @@ mrb_compile_file(mrb_state * mrb, FILE *f)
 }
 
 int
-mrb_compile_nstring(mrb_state *mrb, char *s, int len)
+mrb_compile_nstring(mrb_state *mrb, const char *s, int len)
 {
   parser_state *p;
   int n;
@@ -4828,7 +4828,7 @@ mrb_compile_nstring(mrb_state *mrb, char *s, int len)
 }
 
 int
-mrb_compile_string(mrb_state *mrb, char *s)
+mrb_compile_string(mrb_state *mrb, const char *s)
 {
   return mrb_compile_nstring(mrb, s, strlen(s));
 }