Handle cases such as -xc, i.e no space between x and c.
Add test for unloading of vtables coming from a pch/pcm.
Remove the pch. It is generated by the test.
Add a test exposing an issue with the unloading of inlined functions coming from a pch/pcm.
Move the pch input file in Inputs folder.
Fix cling teardown issues when a pch is attached. Kudos to Axel.
Revert "Fix cling tear down crash involving the ExternalSemaSource."

This reverts commit d320b74acf5172f62b8ac565955ea6497688d225.
We do not own our ExternalSemaSource, it is ref-owned by Sema and ASTContext.