Fix reading options files on platforms with unsigned char

This fixes EOF detection on platforms where char is unsigned, as
comparing it with EOF could never return true there.

Thanks gcc for the warning "comparison is always true due to limited
range of data type [-Wtype-limits]".

Author: vadz

Source/Modules/swigmain.cxx

@@ -163,7 +163,7 @@ static void merge_options_files(int *argc, char ***argv) {
   i = 1;
   while (i < new_argc) {
     if (new_argv[i] && new_argv[i][0] == '@' && (f = fopen(&new_argv[i][1], "r"))) {
-      char c;
+      int ci;
       char *b;
       char *be = &buffer[BUFFER_SIZE];
       int quote = 0;
@@ -174,7 +174,8 @@ static void merge_options_files(int *argc, char ***argv) {
       insert = i;
       b = buffer;
 
-      while ((c = fgetc(f)) != EOF) {
+      while ((ci = fgetc(f)) != EOF) {
+        const char c = static_cast<char>(ci);
         if (escape) {
           if (b != be) {
             *b = c;