Cleanup and bugfixes

- Rebase to latest binutils and gcc sources.
- Simplify function prologue/epilogue generation. Take ideas from 80952abf70dece4ba9a633ce4f08baf557a73d7e.
- Simplify the addsi insn. No more ugly add/adc/adc/adc hacks.
- Current trampoline handling is broken, so marked it as disabled.
- Attempted to fix computed goto computation. See http://gcc.gnu.org/bugzilla/show_bug.cgi?id=61044
- Caught and fixed some more program memory label markings.
- Removed useless instruction scheduling remnants from the Nios2 port.
- Removed DWARF2 exception handling - it is meaningless for PRU.
- Various cleanups and minor bug fixes.

Signed-off-by: Dimitar Dimitrov <dinuxbg@gmail.com>