At least recent libc++ has a std::string ctor overload without a (defaulted)
Allocator argument (which otherwise causes creation of a temporary Allocator
object and thus a ExprWithCleanups), so in C++17 mode (i.e., with no implicit
move CXXConstructExpr -> MaterializeTemporaryExpr -> CXXBindTemporaryExpr chain
in the way) CellInfo::toString (sw/source/filter/ww8/WW8TableInfo.cxx) has a
ReturnStmt of just

> ReturnStmt
> `-ImplicitCastExpr 'std::string':'class std::__1::basic_string<char>' <ConstructorConversion>
>   `-CXXConstructExpr 'std::string':'class std::__1::basic_string<char>' 'void (const char *)'
>     `-ImplicitCastExpr 'const char *' <NoOp>
>       `-ImplicitCastExpr 'char *' <ArrayToPointerDecay>
>         `-DeclRefExpr 'char [256]' lvalue Var 'sBuffer' 'char [256]'

that erroneously triggered loplugin:passstuffbyref.

Change-Id: I53c8911cb1356560692c003808280a103c399e25
Reviewed-on: https://gerrit.libreoffice.org/45916Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>