[Bug c/90885] GCC should warn about 2^16 and 2^32 and 2^64 [-Wxor-used-as-pow]

[dmalcolm at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90885

--- Comment #25 from David Malcolm <dmalcolm at gcc dot gnu.org> ---
Created attachment 53435
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53435&action=edit
v1 of a patch to implement -Wxor-used-as-pow

This patch implements the warning, but doesn't work well; as noted in the text
it's implemented in the parser, when I think it might have to be implemented in
the lexer.

Attaching it here for reference (and as a backup for my hard drive).