MergeFunctions::mergeTwoFunctions may turn identical functions into a
private unnamed function, which trips `assert(F.hasName())`. Without
assertions, all unnamed functions share an empty-name IR comdat (which
yields no ELF section group per MCContext::getELFSection).
Fix#228820: Just drop comdat for unnamed functions. SanitizerCoverage
then retains the metadata sections via `llvm.used`. It's acceptable to
have redundat metadata sections with discarded associated text sections.
(cherry picked from commit 09b7f9faf6170f6deb7c185cc6219d5741edcba8)
Fangrui Song
195209c5c1