We were implicitly assuming that a function reference could only happen
in an expression, ignoring the case of
import func Module.fooFunc
For now, this doesn't actually add the reference to the index because
initCallRefIndexSymbol doesn't allow references without a parent
expression. We can look at adding the reference, or maybe doing
something special to the import itself separately.
rdar://problem/26496135
The code goes into its own sub-tree under 'tools' but tests go under 'test',
so that running 'check-swift' will also run all the SourceKit tests.
SourceKit is disabled on non-darwin platforms.
