[Code]
type
  TTargetPlatform = (x86, x64);
  TTargetPlatforms = set of TTargetPlatform;

procedure InstallVCRedist2013(Platforms: TTargetPlatforms);
begin
  // if we requested x64 version, Windows is 64-bit and there's no x64 version of VC runtime, then...
  if (x64 in Platforms) and IsWin64 and not VCVersionInstalled(VC_2013_REDIST_x64) then
  begin
    // AddProduct for the x64 version here
    AddProduct(64-bit...);
    // we exit this function since the x64 version is going to be installed and your code currently
    // installs only one of them (in case of target_x64x86_Either == True)
    Exit;
  end;
  // either only x86 was requested, or Windows is not 64-bit, or x64 version of VC runtime is already
  // installed (because if the x64 was added for installation, we exit the function); in this case...
  if (x86 in Platforms) and not VCVersionInstalled(VC_2013_REDIST) then
  begin
    // AddProduct for the x86 version here
    AddProduct(32-bit...);
  end;
end;

// and possible calls of the function...
InstallVCRedist2013([x86]);
InstallVCRedist2013([x64]);
InstallVCRedist2013([x86, x64]);