message: Fix symbols.enable-external-lookup description wording
  D55859 changed "external tools or libraries" to "external sources" according to
  Pavel Labath.  Now it is changed sort of back to "external tools and
  repositories" according to Adrian Prantl.
diff: @@ -69,10 +69,10 @@ namespace {
  static constexpr PropertyDefinition g_properties[] = {
  {"enable-external-lookup", OptionValue::eTypeBoolean, true, true, nullptr,
  {},
  - "Control the use of external sources to locate symbol files. "
  - "Directories listed in target.debug-file-search-paths and directory of "
  - "the executable are always checked first for separate debug info files. "
  - "Then depending on this setting: "
  + "Control the use of external tools and repositories to locate symbol "
  + "files. Directories listed in target.debug-file-search-paths and "
  + "directory of the executable are always checked first for separate debug "
  + "info files. Then depending on this setting: "
  "On macOS, Spotlight would be also used to locate a matching .dSYM "
  "bundle based on the UUID of the executable. "
  "On NetBSD, directory /usr/libdata/debug would be also searched. "
  