[dwarf2cfi] Generate remember/restore_state.

[Richard Henderson <rth at redhat dot com>]

Fixes an (intentional) .eh_frame size regression from
before the rewrite.

Without any actual shrink-wrapping, there are not many
differences around the function.  If two traces do
differ, it's easy to look back to the beginning of the
previous trace, which is probably an epilogue, and
emit the remember/restore around the previous trace.

Once we actually do some shrink-wrapping, we can look
back and see if a more complex algorithm is warranted.

Tested on x86_64 and i686 linux.


r~

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