...where CompilerTest_compilerplugins_clang failed in
compilerplugins/clang/test/useuniqueptr.cxx due to Foo24's

  HTMLAttrs::const_iterator it = m_aSetAttrTab.begin();

and either the old compiler lacked Clang's recent
<https://reviews.llvm.org/D50666> "Fix Stmt::ignoreImplicit" (and the above
initialization expression happens to include a CXXBindTemporaryExpr, at least
with libstdc++), or an even older compiler was used in pre-C++17 mode, so the
above initialization expression happens to include an elidable CXXConstructExpr
copy constructor call.

Change-Id: I757a9ad76829e399b4fe2da1c82863909b8c9657
Reviewed-on: https://gerrit.libreoffice.org/61531
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>