[BlockList] Don't share the SourceManager in BlockListStore

BlockListStore doesn't need to keep the buffer after the block-list is
parsed. Don't share the same source manager as the compilation so it
doesn't need to make sure the buffer is valid during the entire duration
of the compilation.

rdar://137448231

Author: cachemeifyoucan

lib/Basic/BlockList.cpp

@@ -19,7 +19,7 @@
 #include "swift/Basic/SourceManager.h"
 
 struct swift::BlockListStore::Implementation {
-  SourceManager &SM;
+  SourceManager SM;
   llvm::StringMap<std::vector<BlockListAction>> ModuleActionDict;
   llvm::StringMap<std::vector<BlockListAction>> ProjectActionDict;
   void addConfigureFilePath(StringRef path);
@@ -45,7 +45,7 @@ struct swift::BlockListStore::Implementation {
     return std::string();
   }
 
-  Implementation(SourceManager &SM) : SM(SM) {}
+  Implementation(SourceManager &SM) : SM(SM.getFileSystem()) {}
 };
 
 swift::BlockListStore::BlockListStore(swift::SourceManager &SM)