[CMake] Fix weiredness in swift runtime linking for SourceKit libraries
SourceKit components are never built while bootstrapping stages. So it
doen't need to have stage 0 or 1 handling.
(cherry picked from commit 914a6fdf7aad9927018940b2c806f1492a4fc938)
(cherry picked from commit 42360db2a875b4257a76985999e886b4234fee25)