tccelf: some linker cleanup

- generate and use SYM@PLT for plt addresses
- get rid of patch_dynsym_undef hack (no idea what it did on FreeBSD)
- use sym_attrs instead of symtab_to_dynsym
- special case for function pointers into .so on i386
- libtcc_test: test tcc_add_symbol with data object
- move target specicic code to *-link.c files
- add R_XXX_RELATIVE (needed for PE)

libtcc.c

@@ -941,7 +941,6 @@ LIBTCCAPI void tcc_delete(TCCState *s1)
     tcc_run_free(s1);
 #endif
 
-    tcc_free(s1->sym_attrs);
     tcc_free(s1);
     tcc_memstats(bench);
 }