When a module built with -autolink-force-load is imported, add a reference
to a special symbol in the corresponding library so that ld is forced to
link it.
This means the library will be linked into the final binary even if no other
symbols are used (which happens for some of our overlays that just add
category methods to Objective-C classes).
Second part of <rdar://problem/16829587>
Swift SVN r17751
This is useful in -i and REPL modes, which do not have a separate linking
step. This version of the -l flag doesn't rely on TranslationUnit. I also
cleaned up the library-loading diagnostics.
Swift SVN r9488
...and use it to load frameworks and libraries in immediate modes (-i and
the REPL), replacing a walk of visible modules that checked if any imported
modules were Clang modules.
Swift SVN r7488
