Synchronize globally-cached code completion results with the results

Synchronize globally-cached code completion results with the results
provided when the optimization is disabled. In particular, split
the completion context CCC_Other into two contexts: CCC_Other, which
means that it's an undisclosed context for which any other results are
unwelcome, and CCC_Recovery, which is used in recovery cases.

Since we're now using the completion context within the completion
results builder, make sure that it's always set to something.

Fixes <rdar://problem/8470644>.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@114704 91177308-0d34-0410-b5e6-96231b3b80d8