Fix PR34668 - P0704R1 implementation is too permissive

Summary:
https://bugs.llvm.org/show_bug.cgi?id=34668

Pretty straightforward.

Reviewers: rsmith, Rakete1111

Reviewed By: Rakete1111

Subscribers: Rakete1111, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D38075

llvm-svn: 337017