[RFA] Compact EH Patch

["Moore, Catherine" <Catherine_Moore at mentor dot com>]

This patch implements a more compact format for exception handling data.  Although I don't have recent numbers for the amount of compression achieved, an earlier measurement showed a 30% reduction in the size of EH data for libstdc++. 

A design document detailing the new format is available (https://github.com/MentorEmbedded/cxx-abi/blob/master/MIPSCompactEH.pdf).

This implementation enables the new format for MIPS targets only, but the generic pieces to enable the new format for other architectures is in place.
I couldn't really think of a good way to split up the patch to make the review easier, but I am open to suggestions.
I've successfully bootstrapped with the patch and completed testing across many of the MIPS targets and multilibs.
I also ran a test series for the x86 without regressions.
Thanks,
Catherine

Attachment: compact-eh.cl
Description: compact-eh.cl

Attachment: compact-eh.patch
Description: compact-eh.patch