[GOLD] PowerPC recreate eh_frame for stubs on each relax pass
There is a very small but non-zero probability that a stub group
contains stubs on one relax pass, but does not on the next. In that
case we would get an FDE covering a zero length address range.
(Actually, it's even worse. Alignment padding for stubs can mean the
address for the non-existent stubs is past the end of the original
section to which stubs are attached, and due to the way
do_plt_fde_location calculates the length we can get a negative
length.) Fixing this properly requires removing the FDE.
Also, I have been implementing the __tls_get_addr_opt support for
gold, and that stub needs something other than the default FDE. The
necessary FDE will depend on the offset to the __tls_get_addr_opt
stub, which of course can change during relaxation. That means at the
very least, rewriting the FDE on each pass, possibly changing the FDE
size. I think that is better done by completely recreating PLT
eh_frame FDEs.