New CRAN warning: identifier preceded by whitespace in a literal operator declaration

[andrjohns]

Hi All,

CRAN has started flagging a new significant warning in the cpp11 headers:

Found the following significant warnings:
  ../inst/include/cpp11/R.hpp:54:31: warning: identifier '_xl' preceded by whitespace in a literal operator declaration is deprecated [-Wdeprecated-literal-operator]
  ../inst/include/cpp11/named_arg.hpp:44:29: warning: identifier '_nm' preceded by whitespace in a literal operator declaration is deprecated [-Wdeprecated-literal-operator]

Here's the relevant checking and install log

The fix is simple enough (changing the declaration from operator"" _xl to operator""_xl), but just flagging here for awareness

Thanks!