Fix a symbol table handling bug in elfcopy: elfcopy puts .symtab,
.strtab and .shstrtab sections in the end of the output object.  If
the input objects have more sections after any of these 3 sections,
the section table will be reordered, and in that case the section
symbols should be regenerated for relocations.

The bug is triggered since newer clang puts .strtab section in the
beginning of the object produced.

 Ticket: #525