Mark the file entry invalid, until reread. Invalidate the SLocEntry cache and readd it on reread.
If the content cache of the SLocEntry is gone, the file was unloaded.
Simplify unloading of files, by delegating to cling.
Files that are .x-ed must be unloadable too. Simplify.
Adapt the user of invalidateCache to its new signature.
Note: this might be change of behavior, because the new implementation doesn't
erase the entry from the ADT.
Skip removing the system function _Unwind_Resume, needed by the JIT.
Adapt to the new (non-const) interface.