Fix build error on Windows old rel (gcc 4.9.3)

[jefferis]

No description provided.

[jefferis]

There were some code sections in the Draco lib conditioned on the DRACO_OLD_GCC, which I was not setting.

One of them in stdio_file_writer.cc caused trouble as below. Rather than using Makevars, I figured that it would be easier to put it in a test in draco_features.h.

d:/Compiler/gcc-4.9.3/mingw_32/bin/g++ -std=gnu++11  -I"D:/RCompile/recent/R-3.6.3/include" -DNDEBUG -I. -I"d:/RCompile/CRANpkg/lib/3.6/Rcpp/include"   -I"d:/Compiler/gcc-4.9.3/local330/include"     -O2 -Wall  -mtune=core2 -c sequential_quantization_attribute_decoder.cc -o sequential_quantization_attribute_decoder.o
d:/Compiler/gcc-4.9.3/mingw_32/bin/g++ -std=gnu++11  -I"D:/RCompile/recent/R-3.6.3/include" -DNDEBUG -I. -I"d:/RCompile/CRANpkg/lib/3.6/Rcpp/include"   -I"d:/Compiler/gcc-4.9.3/local330/include"     -O2 -Wall  -mtune=core2 -c shannon_entropy.cc -o shannon_entropy.o
d:/Compiler/gcc-4.9.3/mingw_32/bin/g++ -std=gnu++11  -I"D:/RCompile/recent/R-3.6.3/include" -DNDEBUG -I. -I"d:/RCompile/CRANpkg/lib/3.6/Rcpp/include"   -I"d:/Compiler/gcc-4.9.3/local330/include"     -O2 -Wall  -mtune=core2 -c stdio_file_reader.cc -o stdio_file_reader.o
d:/Compiler/gcc-4.9.3/mingw_32/bin/g++ -std=gnu++11  -I"D:/RCompile/recent/R-3.6.3/include" -DNDEBUG -I. -I"d:/RCompile/CRANpkg/lib/3.6/Rcpp/include"   -I"d:/Compiler/gcc-4.9.3/local330/include"     -O2 -Wall  -mtune=core2 -c stdio_file_writer.cc -o stdio_file_writer.o
stdio_file_writer.cc: In static member function 'static std::unique_ptr<draco::FileWriterInterface> draco::StdioFileWriter::Open(const string&)':
stdio_file_writer.cc:47:10: error: cannot bind 'std::unique_ptr<draco::StdioFileWriter>' lvalue to 'std::unique_ptr<draco::StdioFileWriter>&&'
   return file;
          ^
In file included from D:/Compiler/gcc-4.9.3/mingw_32/i686-w64-mingw32/include/c++/memory:81:0,
                 from draco/io/stdio_file_writer.h:6,
                 from stdio_file_writer.cc:1:
D:/Compiler/gcc-4.9.3/mingw_32/i686-w64-mingw32/include/c++/bits/unique_ptr.h:220:2: note: initializing argument 1 of 'std::unique_ptr<_Tp, _Dp>::unique_ptr(std::unique_ptr<_Up, _Ep>&&) [with _Up = draco::StdioFileWriter; _Ep = std::default_delete<draco::StdioFileWriter>; <template-parameter-2-3> = void; _Tp = draco::FileWriterInterface; _Dp = std::default_delete<draco::FileWriterInterface>]'
  unique_ptr(unique_ptr<_Up, _Ep>&& __u) noexcept
  ^
stdio_file_writer.cc:51:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
make[1]: *** [stdio_file_writer.o] Error 1
make[1]: Leaving directory `/cygdrive/d/temp/Rtmp4QMo19/R.INSTALL1a5fc58e5723e/dracor/src-i386'
ERROR: compilation failed for package 'dracor'
* removing 'd:/Rcompile/CRANpkg/lib/3.6/dracor'

[jefferis]

So the win-oldrelease build error was actually fixed by removing one of the excess source files.

[jefferis]

But also added support for the DRACO_OLD_GCC macro in f9f81b9