rewrite BCD code

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6055 4407c894-4637-0410-b4f5-ada5f102cad1
Very basic %{H,D,DD}{g,G} printf support

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6056 4407c894-4637-0410-b4f5-ada5f102cad1
%DDE with naive precision control

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6057 4407c894-4637-0410-b4f5-ada5f102cad1
workaround for 0 precision in %DDE precision control

git-svn-id: https://svn.code.sf.net/p/mingw-w64/code@6058 4407c894-4637-0410-b4f5-ada5f102cad1