PLI 1 was deprecated in 1364-2005, so disable by default and note that
it is deprecated in the help text.
This works round the problem that the clang linker (lld) in MSYS2 does
not support the -r option, so cannot be used to build libveriuser.a.
The clang dlltool is not compatible with the binutils dlltool. However
both the clang and binutils linkers support reading the .def file and
creating the import library directly, so we no longer need to perform
the link in two stages.
There are C++11 constructs in Icarus at the moment and the plan is to
retain C++11 compatibility until more modern versions are widely available
in the default installation of systems.
Pass `-std=c++11` to the compile to enforce building with C++11, this will
make sure that neither an older nor a newer version is used. E.g. compilers
on some platforms still default to an earlier version of C++11.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>