Re-introduce correct include directories search path when building standalone Cling on Windows
Optimization: check against previous file name and use its FileEntry.
Fix compilation errors on Windows (constexpr is not known by standard MSVC compiler)
Determing cling location from script location.
-Xclang -x is insufficient; add -c - at the end (-x is position dependent).
Rewire redecl chains if an element gets unloaded.
Mention current failure rate of Sema unloading tests.
Set FE cache, invalid (=null) FE is a reasonable cached value, too.