Adapt Upstream Object's Costomizable Fields

flame/blis#583 introdues 4 additional user customizable function fields.
As BLIS.jl was using an outdated duplication of blis.h:obj_t, upgrading
blis_jll v0.8.1 would cause the whole BLAS interface to break down.
This commit should resolve #9

Author: xrq-phys

src/backend_object/object.jl

@@ -29,6 +29,13 @@ mutable struct BliObjBase
     m_panel::BliDim
     n_panel::BliDim
 
+    # Additional fields from upstream flame/blis#583.
+    # Currently these customizable fields have no Julia interface.
+    pack_fn::Ptr{Nothing}
+    pack_params::Ptr{Nothing}
+    ker_fn::Ptr{Nothing}
+    ker_params::Ptr{Nothing}
+
     # Empty inner-constructor only,
     #  resembling a plain C struct.
     BliObjBase() = begin