cmake: Only export targets in the standalone build

Trying to fix bots that didn't like the fact that I exported targets
that depended on LLVM without exporting targets from LLVM.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@221415 91177308-0d34-0410-b5e6-96231b3b80d8
Patch for small addition to availability attribute.
This is to accept "NA" in place of vesion number for availability
attribute. Used on introduced=NA to mean unavailable
and deprecated=NA to mean nothing (not deprecated).
rdar://18804883


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@221417 91177308-0d34-0410-b5e6-96231b3b80d8