Allow users of the GCOV API to extend the FileInfo class to implement custom output formats

[marco-c]

Summary

The GCOV API can be used to parse gcda/gcno files, but in order to implement custom output formats, users need to reimplement everything.
If the FileInfo members were protected instead of private, they'd be able to reuse the code.

[davide]

I don't mind this change, but before accepting, can you please show the other bits? (i.e. how do you plan to use these?)

Thanks!

[marco-c]

Here's an example usage of this: https://github.com/marco-c/grcov/blob/5607a99f32748de23cf96ebbfe4edf3e2197a9cf/src/c/llvmgcov.cpp#L8

llvm/trunk/include/llvm/ProfileData/GCOV.h

private:
   uint64_t Counter = 0;
   bool DstEdgesAreSorted = true;
   SmallVector<GCOVEdge *, 16> SrcEdges;
   SmallVector<GCOVEdge *, 16> DstEdges;
   SmallVector<uint32_t, 16> Lines;
 };
 
 class FileInfo {
+protected:
   // It is unlikely--but possible--for multiple functions to be on the same
   // line.
   // Therefore this typedef allows LineData.Functions to store multiple
   // functions
   // per instance. This is rare, however, so optimize for the common case.
   using FunctionVector = SmallVector<const GCOVFunction *, 1>;
   using FunctionLines = DenseMap<uint32_t, FunctionVector>;
   using BlockVector = SmallVector<const GCOVBlock *, 4>;
void addFunctionLine(StringRef Filename, uint32_t Line,
     LineInfo[Filename].Functions[Line - 1].push_back(Function);
   }
 
   void setRunCount(uint32_t Runs) { RunCount = Runs; }
   void setProgramCount(uint32_t Programs) { ProgramCount = Programs; }
   void print(raw_ostream &OS, StringRef MainFilename, StringRef GCNOFile,
              StringRef GCDAFile);
 
-private:
+protected:
   std::string getCoveragePath(StringRef Filename, StringRef MainFilename);
   std::unique_ptr<raw_ostream> openCoveragePath(StringRef CoveragePath);
   void printFunctionSummary(raw_ostream &OS, const FunctionVector &Funcs) const;
   void printBlockInfo(raw_ostream &OS, const GCOVBlock &Block,
                       uint32_t LineIndex, uint32_t &BlockNo) const;
   void printBranchInfo(raw_ostream &OS, const GCOVBlock &Block,
                        GCOVCoverage &Coverage, uint32_t &EdgeNo);
   void printUncondBranchInfo(raw_ostream &OS, uint32_t &EdgeNo,