Blender Git Loki

For gcc based systems use g++ for linking. This is necessary so that exceptions are propagated between shared libraries. We already use g++ when linking with cmake.

This solves crash when trying to render with missing files on MinGW-w64 cycles. The cause was an OpenEXR exception that went uncaught when trying to check the file's extension through OpenImageIO while building the shader tree. Thus my bug-hunting frustration can end with a happy chord.