Better handle ld scripts

* search file from INPUT and GROUP commands in the library path in
  addition to the current directory
* handle libraries specified by -lfoo options
* Search lib in GROUP command repeatedly

tcc.h

@@ -225,6 +225,8 @@ typedef struct Sym {
     struct Sym *prev_tok; /* previous symbol for this token */
 } Sym;
 
+static int new_undef_sym = 0; /* Is there a new undefined sym since last new_undef_sym() */
+
 /* section definition */
 /* XXX: use directly ELF structure for parameters ? */
 /* special flag to indicate that the section should not be linked to