Compiler: Add #warning directive.

Basically same as error but as warning.
Imported from SA-MP: 1bd6be93e0

Example:

  #warning don't eat egg.

Result:

  warning.sma(1) : warning 234: user warning: don't eat egg.

compiler/libpc300/sc5-in.scp

@@ -238,7 +238,7 @@ static char *fatalmsg[] = {
 /*108*/  "codepage mapping file not found\n",
 /*109*/  "invalid path: \"%s\"\n",
 /*110*/  "assertion failed: %s\n",
-/*111*/  "user error: %s\n",
+/*111*/  "user error: %s\n"
 #else
   "c\224\241\222a\206from \327le\335",
   "c\224\241writ\200\277 \327le\335",
@@ -291,6 +291,7 @@ static char *warnmsg[] = {
 /*231*/  "state specification on forward declaration is ignored\n",
 /*232*/  "output file is written, but with compact encoding disabled\n"
 /*233*/  "symbol \"%s\" is marked as deprecated: %s\n",
+/*234*/  "user warning: %s\n"
 #else
   "\345 \274tr\240\226\233\277 %\206\273\337c\367\305",
   "\222\323i\231\300\344\224t/\314cr\375\364",