CWG3194 [lex.pptoken] Lexing of <=> #910

Full name of submitter (unless configured in github; will be published with the issue): Jay Ghiron

Reference (section label): [lex.pptoken]/5

Issue description:

#include<=>

Is this <=> parsed as a punctuator or as a header-name? The wording does not seem to specify which it is.

Suggested resolution:

Modify [lex.pptoken]/5.4.1:

a string-literal preprocessing token is never formed when a header-name preprocessing token can be formed, and

Create a new bullet after [lex.pptoken]/5.4.1:

a <=> punctuator preprocessing token is never formed when a header-name preprocessing token can be formed, and