Revert "[clang] Avoid memcopy for small structure with padding under...

Revert "[clang] Avoid memcopy for small structure with padding under -ftrivial-auto-var-init (#71677)"

This reverts commit fe5c360a.
The commit causes the tests below to fail on many buildbots, e.g.
https://lab.llvm.org/buildbot/#/builders/245/builds/17047

  Clang :: CodeGen/aapcs-align.cpp
  Clang :: CodeGen/aapcs64-align.cpp