Revert "[Modules] Remove unnecessary check when generating name lookup table in ASTWriter"

This reverts commit bc95f273, originally db987b95.
clang/test/Modules/pr61065.cppm is retained to make relands show less diff.

There are other module-related issues that were not caught, related to
false positive errors like
"error: no matching constructor for initialization of 'union (anonymous union at ..."

Reopen #61065