tccpp: alternative fix for #include_next infinite loop bug

This replaces commit 3d409b0889

- revert old fix in libtcc.c
- #include_next: look up the file in the include stack to see
  if it is already included.
Also:
- streamline include code
- remove 'type' from struct CachedInclude (obsolete because we check
  full filename anyway)
- remove inc_type & inc_filename from struct Bufferedfile (obsolete)
- fix bug with TOK_FLAG_ENDIF not being reset
- unrelated: get rid of an 'variable potentially uninitialized' warning

libtcc.c

@@ -34,10 +34,6 @@ ST_DATA struct TCCState *tcc_state;
 
 /********************************************************/
 
-#ifndef _WIN32
-#include <limits.h>
-#endif
-
 #ifdef ONE_SOURCE
 #include "tccpp.c"
 #include "tccgen.c"
@@ -322,30 +318,7 @@ static void tcc_split_path(TCCState *s, void ***p_ary, int *p_nb_ary, const char
             }
         }
         cstr_ccat(&str, '\0');
-#ifndef _WIN32
-        {
-            int i, do_include;
-            char tmp[PATH_MAX];
-
-            if (realpath(str.data, tmp)) {
-                str.size = 0;
-                cstr_cat(&str, tmp);
-                cstr_ccat(&str, '\0');
-            }
-
-            do_include = 1;
-            for (i = 0; i < *p_nb_ary && do_include; i++) {
-                do_include = do_include &&
-                    strcmp((char*)str.data, (char*)(*p_ary)[i]);
-            }
-
-            if (do_include) {
-                dynarray_add(p_ary, p_nb_ary, str.data);
-            }
-        }
-#else
         dynarray_add(p_ary, p_nb_ary, str.data);
-#endif
         in = p+1;
     } while (*p);
 }