Convert the exception-freeing cleanup over to the conditional cleanups code,

Convert the exception-freeing cleanup over to the conditional cleanups code,
fixing a crash which probably nobody was ever going to see.  In doing so,
fix a horrendous number of problems with the conditional-cleanups code.
Also, make conditional cleanups re-use the cleanup's activation variable,
which avoids some unfortunate repetitiveness.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@124481 91177308-0d34-0410-b5e6-96231b3b80d8