Oops, does not actually fix this issue.

The diagnostic has always appeared on Windows and never on Linux, and
that hasn't changed with this patch.

Author: AaronBallman

clang/test/C/C23/n3037.c

@@ -359,9 +359,3 @@ struct alignment { // c17-error {{redefinition of 'alignment'}} \
                       c23-error {{type 'struct alignment' has a member with an attribute which currently causes the types to be treated as though they are incompatible}}
   int x;
 };
-
-// Previously, this code was silently accepted by Clang despite the
-// incompatible redefinitions. This is now correctly being caught.
-unsigned GH28586;           // both-note 2 {{previous definition is here}}
-enum { GH28586_1 } GH28586; // both-error-re {{redefinition of 'GH28586' with a different type: 'enum (unnamed enum at {{.*}})' vs 'unsigned int'}}
-enum { GH28586_2 } GH28586; // both-error-re {{redefinition of 'GH28586' with a different type: 'enum (unnamed enum at {{.*}})' vs 'unsigned int'}}