fix compilation error in C++ mode on Solaris 11 OpenIndiana

A testdir built with ./gnulib-tool --create-testdir --dir=../testdir1 --single-configure --with-c++-tests `./posix-modules` does not compile on Solaris 11 OpenIndiana: depbase=`echo test-wchar-c++.o | sed 's|[^/]*$|.deps/&|;s|\.o$||'`;\ g++ -m64 -O2 -U_XOPEN_SOURCE -D_XOPEN_SOURCE=700 -DHAVE_CO

fix compilation errors in C++ mode with xlclang++ on AIX

Christian Biesinger wrote: > (tested on the GCC compile farm, gcc119, /opt/IBM/xlC/16.1.0/bin/xlclang++) First, we need to make sure that gnulib basically works fine on this platform. To this effect, I build a testdir ./gnulib-tool --create-testdir --dir=../testdir1 --single-configure --with-c