RTTI support in devel/llvm40 (and maybe other llvm ports)

[Alexey Dokuchaev]

On Sun, Nov 12, 2017 at 02:01:39PM +1030, Shane Ambler wrote:
> On 10/11/2017 17:37, Alexey Dokuchaev wrote:
> > I've just found out that our `devel/llvm40' port comes without
> > -DLLVM_ENABLE_RTTI=ON on the CMAKE_ARGS.  This is a regression
> > from e.g. 3.4 times when it was enabled by default.
> > 
> > The problem is that RTTI support is required by some consumers,
> > e.g. `graphics/openshadinglanguage' and `graphics/appleseed'
> > (cf. https://github.com/appleseedhq/appleseed/issues/1625),
> > but I cannot enable RTTI in those ports unless I enable it in
> > LLVM port(s) first.
> [...]
> 
> While I know appleseed fails when rtti is disabled directly in CXXFLAGS,
> maybe cmake can detect the use of rtti in llvm (or offer an option) and
> adjust to suit, or just add -fno-rtti only for the osl files.

According to Esteban (one of appleseed's devs), they do use RTTI, so
disabling it is not an option (see discussion in that issue #1625).

Also, from the point of feature-completeness of infrastructure-important
port(s) such as LLVM, having RTTI enabled by default looks good to me.

./danfe