Fix --gc-sections for C++ MIPS ELF

[Richard Sandiford]

Alan Modra <amodra@bigpond.net.au> writes:
> This all looks reasonable to me.  OK to apply.

Applied.  Thanks for reviewing that lot. ;)  For the record,
I added an explicit:

  /* Unused bits.  */
  unsigned int pad1 : 4;

to eh_cie_fde to try to make sure that the new :8 bitfields were
byte-aligned on all hosts.  That was the only change from the
posted patches.

Please shout if you find a problem.

Richard