Blender Git Loki

Buildbot: Ensure proper ABI is used

This wasn't an issue in the real buildbot environment since the
precompiled libraries are compiled with same ABI as the compiler
used for Blender build. But it was causing issues when building
Blender using buildbot scripts (for troubleshooting purposes)
on a machine with different default compiler ABI.

Usually ABI detection is happening in platform_unix.cmake when
detecting whether there are any precompiled libraries folder
available. This detection is not happening when library folder
is provided explicitly, expecting ABI to be setup explicitly
as well.