Revert "Fix -pthread option handling"

This reverts commit 3f8225509b.
It fixes the linking case but introduces an ugly error with -c
about adding a library.  To fix both uses the old code structure is
better.

libtcc.c

@@ -1742,14 +1742,13 @@ reparse:
             tcc_set_lib_path(s, optarg);
             break;
         case TCC_OPTION_l:
-add_lib:
             args_parser_add_file(s, optarg, AFF_TYPE_LIB);
             s->nb_libraries++;
             break;
         case TCC_OPTION_pthread:
             parse_option_D(s, "_REENTRANT");
-	    optarg = "pthread";
-	    goto add_lib;
+            s->option_pthread = 1;
+            break;
         case TCC_OPTION_bench:
             s->do_bench = 1;
             break;

tcc.c

@@ -297,6 +297,9 @@ redo:
                 tcc_error("cannot specify libraries with -c");
             if (n > 1 && s->outfile)
                 tcc_error("cannot specify output file with -c many files");
+        } else {
+            if (s->option_pthread)
+                tcc_set_options(s, "-lpthread");
         }
 
         if (s->do_bench)

tcc.h

@@ -817,6 +817,7 @@ struct TCCState {
     int do_bench; /* option -bench */
     int gen_deps; /* option -MD  */
     char *deps_outfile; /* option -MF */
+    int option_pthread; /* -pthread option */
     int argc;
     char **argv;
 };