message: Allow usage of os="windows" in vcpkgTools.xml from vcpkg.exe
  (use-cases in powershell still need to be modified)
diff: @@ -44,11 +44,11 @@ namespace vcpkg
  static ToolData parse_tool_data_from_xml(const VcpkgPaths& paths, const std::string& tool)
  {
  #if defined(_WIN32)
  - static constexpr StringLiteral OS_STRING = "";
  + static constexpr StringLiteral OS_STRING = "windows";
  #elif defined(__APPLE__)
  - static constexpr StringLiteral OS_STRING = R"(os="osx")";
  + static constexpr StringLiteral OS_STRING = "osx";
  #else // assume linux
  - static constexpr StringLiteral OS_STRING = R"(os="linux")";
  + static constexpr StringLiteral OS_STRING = "linux";
  #endif
  static const fs::path XML_PATH = paths.scripts / "vcpkgTools.xml";
  @@ -79,11 +79,16 @@ namespace vcpkg
  Strings::format(R"###(<archiveRelativePath>([\s\S]*?)</archiveRelativePath>)###")};
  static const std::regex URL_REGEX{Strings::format(R"###(<url>([\s\S]*?)</url>)###")};
  - const std::regex tool_regex{
  - Strings::format(R"###(<tool[\s]+name="%s"[\s]*%s>([\s\S]*?)</tool>)###", tool, OS_STRING)};
  + std::regex tool_regex{
  + Strings::format(R"###(<tool[\s]+name="%s"[\s]+os="%s">([\s\S]*?)<\/tool>)###", tool, OS_STRING)};
  std::smatch match_tool;
  - const bool has_match_tool = std::regex_search(XML.cbegin(), XML.cend(), match_tool, tool_regex);
  + bool has_match_tool = std::regex_search(XML.cbegin(), XML.cend(), match_tool, tool_regex);
  + if (!has_match_tool && OS_STRING == "windows") // Legacy support. Change introduced in vcpkg v0.0.107.
  + {
  + tool_regex = Strings::format(R"###(<tool[\s]+name="%s">([\s\S]*?)<\/tool>)###", tool);
  + has_match_tool = std::regex_search(XML.cbegin(), XML.cend(), match_tool, tool_regex);
  + }
  Checks::check_exit(VCPKG_LINE_INFO,
  has_match_tool,
  "Could not find entry for tool [%s] in %s",
  