[Bug preprocessor/109994] Issue a diagnostic when a C++ file defines a macro that hides a keyword

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109994

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
There are definitly testcases in GCC's testsuite which does this all the time.
#define int ...