Blender Git Loki

Disable IR module loading for blenvm by default (with a compile option).

Base modules for nodes will instead be declared as external functions with regular
linkage through C code. This means some potential for low-level optimization might be lost,
but this shouldn't be a big problem as long as node functions don't get too complex
(which means they should be split up in the first place).

IR module loading is not the real issue, but generating the IR code from C/C++ code
in a generic way is not so easy. In the future we may actually generate most code for
basic operators and types directly inside blenvm and only use precompiled modules
for more complex functions.