warning for meaningless class combinations

1. Adds a generic new warning which is triggered when meaningless combination of class specifiers are used.

2. This commit adds code to trigger a warning for the following two cases:
- constant reference
- - not meaningful as as references always point to cells in PAWN (unlike C++ where it would help costly copies while guaranteeing to not modify the object) which makes const reference is as good as pass-by-value
- constant variable arguments
- - for similar reasons as in the previous case

source/compiler/sc1.c

@@ -3868,6 +3868,8 @@ static int declargs(symbol *sym,int chkshadow)
       case '&':
         if (ident!=iVARIABLE || numtags>0)
           error(1,"-identifier-","&");
+        if (fconst)
+          error(238, "const reference"); /* meaningless combination of class specifiers */
         ident=iREFERENCE;
         break;
       case tCONST:
@@ -3942,6 +3944,8 @@ static int declargs(symbol *sym,int chkshadow)
       case tELLIPS:
         if (ident!=iVARIABLE)
           error(10);                    /* illegal function or declaration */
+        if (fconst)
+          error(238, "const variable arguments"); /* meaningless combination of class specifiers */
         if (numtags==0)
           tags[numtags++]=0;            /* default tag */
         if ((sym->usage & uPROTOTYPED)==0) {

source/compiler/sc5.c

@@ -191,7 +191,8 @@ static char *warnmsg[] = {
 /*234*/  "function is deprecated (symbol \"%s\") %s\n",
 /*235*/  "public function lacks forward declaration (symbol \"%s\")\n",
 /*236*/  "unknown parameter in substitution (incorrect #define pattern)\n",
-/*237*/  "user warning: %s\n"
+/*237*/  "user warning: %s\n",
+/*238*/  "meaningless combination of class specifiers (%s)\n"
 };
 
 #define NUM_WARNINGS    (sizeof warnmsg / sizeof warnmsg[0])