[lld] resolve dylib paths before caching

When loading frameworks it is possible to have load commands for the same
framework through symlinks and the real path. To avoid loading these multiple
times find the real path before checking the dylib cache.

Author: rmaz

lld/MachO/DriverUtils.cpp

@@ -229,7 +229,11 @@ static DenseMap<CachedHashStringRef, DylibFile *> loadedDylibs;
 
 DylibFile *macho::loadDylib(MemoryBufferRef mbref, DylibFile *umbrella,
                             bool isBundleLoader, bool explicitlyLinked) {
-  CachedHashStringRef path(mbref.getBufferIdentifier());
+  // Frameworks can be found from different symlink paths, so resolve
+  // symlinks before looking up in the dylib cache.
+  SmallString<128> realPath;
+  fs::real_path(mbref.getBufferIdentifier(), realPath);
+  CachedHashStringRef path(uniqueSaver().save(StringRef(realPath)));
   DylibFile *&file = loadedDylibs[path];
   if (file) {
     if (explicitlyLinked)