Made prototypes for yyerror() consistent with Bruce's last changes

Jan

src/interfaces/ecpg/preproc/extern.h

@@ -37,7 +37,7 @@ extern void lex_init(void);
 extern char *input_filename;
 extern int	yyparse(void);
 extern int	yylex(void);
-extern void yyerror(char *);
+extern void yyerror(const char * error);
 extern void *mm_alloc(size_t), *mm_realloc(void *, size_t);
 extern char *mm_strdup(const char *);
 extern void mmerror(enum errortype, char * );

src/interfaces/ecpg/preproc/preproc.y

@@ -5428,7 +5428,7 @@ blockend : '}' {
 
 %%
 
-void yyerror(char * error)
+void yyerror(const char * error)
 {
 	mmerror(ET_ERROR, error);
 }