message: Display names of environment variables correctly for non-Windows
  platforms in help
  Currently vcpkg displays environment variable names in the help as
  %VARIABLENAME% on non-Windows platforms, where it should be
  $VARIABLENAME. This patch adds a macro to fix this.
diff: #include <vcpkg/install.h>
  #include <vcpkg/remove.h>
  +// Write environment variable names as %VARIABLE% on Windows and $VARIABLE in *nix
  +#ifdef _WIN32
  +#define ENVVAR(VARNAME) "%%" #VARNAME "%%"
  +#else
  +#define ENVVAR(VARNAME) "$" #VARNAME
  +#endif
  +
  namespace vcpkg::Help
  {
  struct Topic
  @@ -93,7 +100,7 @@ namespace vcpkg::Help
  "%s" // Integration help
  "\n"
  " vcpkg export <pkg>... [opt]... Exports a package\n"
  - " vcpkg edit <pkg> Open up a port for editing (uses %%EDITOR%%, default 'code')\n"
  + " vcpkg edit <pkg> Open up a port for editing (uses " ENVVAR(EDITOR) ", default 'code')\n"
  " vcpkg import <pkg> Import a pre-built library\n"
  " vcpkg create <pkg> <url>\n"
  " [archivename] Create a new package\n"
  @@ -104,10 +111,10 @@ namespace vcpkg::Help
  "\n"
  "Options:\n"
  " --triplet <t> Specify the target architecture triplet.\n"
  - " (default: %%VCPKG_DEFAULT_TRIPLET%%, see 'vcpkg help triplet')\n"
  + " (default: " ENVVAR(VCPKG_DEFAULT_TRIPLET) ", see 'vcpkg help triplet')\n"
  "\n"
  " --vcpkg-root <path> Specify the vcpkg root directory\n"
  - " (default: %%VCPKG_ROOT%%)\n"
  + " (default: " ENVVAR(VCPKG_ROOT) ")\n"
  "\n"
  "For more help (including examples) see the accompanying README.md.",
  Commands::Integrate::INTEGRATE_COMMAND_HELPSTRING);
  