Work around MSVC "friend" semantics.

The error on clang-x86-win2008-selfhost is:

C:\buildbot\slave-config\clang-x86-win2008-selfhost\llvm\lib\Transforms\Vectorize\SLPVectorizer.cpp(955) : error C2248: 'llvm::slpvectorizer::BoUpSLP::ScheduleData' : cannot access private struct declared in class 'llvm::slpvectorizer::BoUpSLP'
        C:\buildbot\slave-config\clang-x86-win2008-selfhost\llvm\lib\Transforms\Vectorize\SLPVectorizer.cpp(608) : see declaration of 'llvm::slpvectorizer::BoUpSLP::ScheduleData'
        C:\buildbot\slave-config\clang-x86-win2008-selfhost\llvm\lib\Transforms\Vectorize\SLPVectorizer.cpp(337) : see declaration of 'llvm::slpvectorizer::BoUpSLP'

I reproduced this locally with both MSVC 2013 and MSVC 2015.

llvm-svn: 272772

llvm/lib/Transforms/Vectorize/SLPVectorizer.cpp

@@ -601,6 +601,7 @@ private:
   /// A list of blocks that we are going to CSE.
   SetVector<BasicBlock *> CSEBlocks;
 
+public: // Workaround for MSVC friend semantics.
   /// Contains all scheduling relevant data for an instruction.
   /// A ScheduleData either represents a single instruction or a member of an
   /// instruction bundle (= a group of instructions which is combined into a
@@ -730,6 +731,7 @@ private:
     /// dry-run).
     bool IsScheduled;
   };
+private:
 
 #ifndef NDEBUG
   friend raw_ostream &operator<<(raw_ostream &os,