meson: fix builds against LLVM built without rtti

Building without rtti is a frought with peril, but it's something that
autotools supports so we need to support it too.

Since we've moved to version 0.44 as a whole we can use the meson
functionality for accessing random llvm-config options we can check for
rtti and add -fno-rtti to all C++ code accordingly.

Signed-off-by: Dylan Baker <dylan.c.baker@intel.com>
1 file changed