Don't declare public constants as constants

Public constants must be declared as variables, like it was done
before the previous commit, because they must be visible by the
amx_XXXPubVar API.

source/compiler/sc1.c

@@ -1861,7 +1861,7 @@ static void declfuncvar(int fpublic,int fstatic,int fstock,int fconst)
     invalidfunc= fconst || (fpublic && fstock);
     if (invalidfunc || !newfunc(name,tag,fpublic,fstatic,fstock)) {
       /* if not a function, try a global constant/variable */
-      if (fconst) {
+      if (fconst && !fpublic) {
         lexpush();
         decl_const(sGLOBAL);
       } else {