Add .cfi_startproc and endproc markers

Helps a bit... Now, if I revert the hackish arm64 change to ucbhelper,
instead of "terminating with uncaught exception" I get "terminating
with unexpected exception";) But, at least with the stack correctly
unwound to BaseContent::execute(), I think. Actually of course I don't
really understand much of this.

Change-Id: Iacb4342414cb84f9db31f9a40c7a136cc5d191a6