This is functionally a revert of
8eeb513b. The language of the extension
is slightly confusing to me, but GL_STREAM_*_ARB is more dynamic than
GL_DYNAMIC_*_ARB. So use GL_STREAM usage for D3DUSAGE_DYNAMIC buffers and
GL_DYNAMIC usage for non-dynamic buffers.

This is just the object used to store the byte code, the shader compiler
doesn't know how to handle geometry shaders yet.