[llvm] [clang] [clang-tools-extra] [flang] [compiler-rt] [clang] Add test for CWG1807 (PR #77637)

[Daniel Thornburgh via cfe-commits]

mysterymath wrote:

It looks like 30da0f5  didn't fully fix this; Fuchsia's Mac toolchain builder just completed a run with this change that still fails that test:
https://luci-milo.appspot.com/ui/p/fuchsia/builders/toolchain.ci/clang-mac-x64/b8758543058445552977/test-results?sortby=&groupby=
https://luci-milo.appspot.com/ui/p/fuchsia/builders/toolchain.ci/clang-mac-x64/b8758543058445552977/blamelist

https://github.com/llvm/llvm-project/pull/77637